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Merge branch 'master' into patch-1

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Angelos Chalaris
2017-12-12 16:05:55 +02:00
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6
CONTRIBUTING.md
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@ -1,13 +1,13 @@
## Contributing
You can cntribute to **30 seconds of code** by sending pull requests for snippets that you find useful, reporting issues with current snippets or suggesting changes and/or additions.
You can contribute to **30 seconds of code** by sending pull requests for snippets that you find useful, reporting issues with current snippets or suggesting changes and/or additions.
### Guidelines for new snippets
- Snippets must be short. Usually anything above 10 lines would be considered too long, but you can still submit it as it might be possible to shorten it or it might still prove useful regardless of its length.
- Snippets must be explain to a certain extent in the description above them. Make sure to include what functions you are using and why.
- Snippets must be explained to a certain extent in the description above them. Make sure to include what functions you are using and why.
- Snippets must solve real-world problems and should be abstract enough to use in different scenarios. This is highly subjective, so send them in anyways.
- Snippets *should* be written in ES6 if possible.
- Snippet files must follow the anchor name conventions of (GitHub Flavored Markdown)[https://github.github.com/gfm/], so that the `builder.js` can build the links for the list.
- Snippet files must follow the anchor name conventions of [GitHub Flavored Markdown](https://github.github.com/gfm/), so that the `builder.js` can build the links for the list.
- Use the [template](snippet-template.md) to format your snippets.
- If possible, provide test cases in your Pull Request (link or comment), so that it's easier to verify that each snippet is working.

214
README.md
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@ -8,11 +8,9 @@
## Contents
* [RGB to hexadecimal](#rgb-to-hexadecimal)
* [URL parameters](#url-parameters)
* [UUID generator](#uuid-generator)
* [Anagrams of string (with duplicates)](#anagrams-of-string-with-duplicates)
* [Average of array of numbers](#average-of-array-of-numbers)
* [Capitalize first letter of every word](#capitalize-first-letter-of-every-word)
* [Capitalize first letter](#capitalize-first-letter)
* [Count occurrences of a value in array](#count-occurrences-of-a-value-in-array)
* [Current URL](#current-url)
@ -23,7 +21,9 @@
* [Even or odd number](#even-or-odd-number)
* [Factorial](#factorial)
* [Fibonacci array generator](#fibonacci-array-generator)
* [Filter out non uniqe values in an array](#filter-out-non-uniqe-values-in-an-array)
* [Flatten array](#flatten-array)
* [Get scroll position](#get-scroll-position)
* [Greatest common divisor (GCD)](#greatest-common-divisor-gcd)
* [Head of list](#head-of-list)
* [Initial of list](#initial-of-list)
@ -36,6 +36,8 @@
* [Random number in range](#random-number-in-range)
* [Randomize order of array](#randomize-order-of-array)
* [Redirect to url](#redirect-to-url)
* [Reverse a string](#reverse-a-string)
* [RGB to hexadecimal](#rgb-to-hexadecimal)
* [Scroll to top](#scroll-to-top)
* [Similarity between arrays](#similarity-between-arrays)
* [Sort characters in string (alphabetical)](#sort-characters-in-string-alphabetical)
@ -43,40 +45,10 @@
* [Swap values of two variables](#swap-values-of-two-variables)
* [Tail of list](#tail-of-list)
* [Unique values of array](#unique-values-of-array)
* [URL parameters](#url-parameters)
* [UUID generator](#uuid-generator)
* [Validate number](#validate-number)
### RGB to hexadecimal
Convert each value to a hexadecimal string, using `toString(16)`, then `padStart(2,'0')` to get a 2-digit hexadecimal value.
Combine values using `join('')`.
```js
var rgbToHex = (r, g, b) =>
[r,g,b].map( v => v.toString(16).padStart(2,'0')).join('');
```
### URL parameters
Use `match()` with an appropriate regular expression to get all key-value pairs, `map()` them appropriately.
Combine all key-value pairs into a single object using `Object.assign()` and the spread operator (`...`).
Pass `location.search` as the argument to apply to the current `url`.
```js
var getUrlParameters = url =>
Object.assign(...url.match(/([^?=&]+)(=([^&]*))?/g).map(m => {[f,v] = m.split('='); return {[f]:v}}));
```
### UUID generator
Use `crypto` API to generate a UUID, compliant with [RFC4122](https://www.ietf.org/rfc/rfc4122.txt) version 4.
```js
var uuid = _ =>
( [1e7]+-1e3+-4e3+-8e3+-1e11 ).replace( /[018]/g, c =>
(c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> c / 4).toString(16)
)
```
### Anagrams of string (with duplicates)
Use recursion.
@ -85,7 +57,7 @@ Use `map()` to combine the letter with each partial anagram, then `reduce()` to
Base cases are for string `length` equal to `2` or `1`.
```js
var anagrams = s => {
const anagrams = s => {
if(s.length <= 2) return s.length === 2 ? [s, s[1] + s[0]] : [s];
return s.split('').reduce( (a,l,i) => {
anagrams(s.slice(0,i) + s.slice(i+1)).map( v => a.push(l+v) );
@ -99,24 +71,34 @@ var anagrams = s => {
Use `reduce()` to add each value to an accumulator, initialized with a value of `0`, divide by the `length` of the array.
```js
var average = arr =>
const average = arr =>
arr.reduce( (acc , val) => acc + val, 0) / arr.length;
```
### Capitalize first letter of every word
Use `replace()` to match the first character of each word and `toUpperCase()` to capitalize it.
```js
const capitalizeEveryWord = str => str.replace(/\b[a-z]/g, char => char.toUpperCase());
```
### Capitalize first letter
Use `toUpperCase()` to capitalize first letter, `slice(1)` to get the rest of the string.
Use `slice(0,1)` and `toUpperCase()` to capitalize first letter, `slice(1)` to get the rest of the string.
Omit the `lowerRest` parameter to keep the rest of the string intact, or set it to `true` to convert to lower case.
```js
var capitalize = str => str[0].toUpperCase() + str.slice(1);
const capitalize = (str, lowerRest = false) =>
str.slice(0, 1).toUpperCase() + (lowerRest? str.slice(1).toLowerCase() : str.slice(1));
```
### Count occurrences of a value in array
Use `filter()` to create an array containing only the items with the specified value, count them using `length`.
Use `reduce()` to increment a counter each time you encounter the specific value inside the array.
```js
var countOccurrences = (arr, value) => arr.filter(v => v === value).length;
const countOccurrences = (arr, value) => arr.reduce((a, v) => v===value ? a + 1 : a + 0, 0);
```
### Current URL
@ -124,7 +106,7 @@ var countOccurrences = (arr, value) => arr.filter(v => v === value).length;
Use `window.location.href` to get current URL.
```js
var currentUrl = _ => window.location.href;
const currentUrl = _ => window.location.href;
```
### Curry
@ -134,27 +116,25 @@ If the number of provided arguments (`args`) is sufficient, call the passed func
Otherwise return a curried function `f` that expects the rest of the arguments.
```js
var curry = f =>
const curry = f =>
(...args) =>
args.length >= f.length ? f(...args) : (...otherArgs) => curry(f)(...args, ...otherArgs)
```
### Difference between arrays
Use `filter()` to remove values that are part of `values`, determined using `indexOf()`.
Use `filter()` to remove values that are part of `values`, determined using `includes()`.
```js
var difference = (arr, values) =>
arr.filter(v => values.indexOf(v) === -1);
const difference = (arr, values) => arr.filter(v => !values.includes(v));
```
### Distance between two points
Use `Math.pow()` and `Math.sqrt()` to calculate the Euclidean distance between two points.
Use `Math.hypot()` to calculate the Euclidean distance between two points.
```js
var distance = x0, y0, x1, y1 =>
Math.sqrt(Math.pow(x1-x0, 2) + Math.pow(y1 - y0, 2))
const distance = (x0, y0, x1, y1) => Math.hypot(x1 - x0, y1 - y0);
```
### Escape regular expression
@ -162,7 +142,7 @@ var distance = x0, y0, x1, y1 =>
Use `replace()` to escape special characters.
```js
var escapeRegExp = s =>
const escapeRegExp = s =>
s.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
}
```
@ -173,16 +153,17 @@ Use `Math.abs()` to extend logic to negative numbers, check using the modulo (`%
Return `true` if the number is even, `false` if the number is odd.
```js
var isEven = num => Math.abs(num) % 2 === 0;
const isEven = num => Math.abs(num) % 2 === 0;
```
### Factorial
Create an array of length `n+1`, use `reduce()` to get the product of every value in the given range, utilizing the index of each element.
Use recursion.
If `n` is less than or equal to `1`, return `1`.
Otherwise, return the product of `n` and the factorial of `n - 1`.
```js
var factorial = n =>
Array.apply(null, [1].concat(Array(n))).reduce( (a, _, i) => a * i || 1 , 1);
const factorial = n => n <= 1 ? 1 : n * factorial(n - 1)
```
### Fibonacci array generator
@ -191,7 +172,7 @@ Create an empty array of the specific length, initializing the first two values
Use `reduce()` to add values into the array, using the sum of the last two values, except for the first two.
```js
var fibonacci = n =>
const fibonacci = n =>
Array.apply(null, [0,1].concat(Array(n-2))).reduce(
(acc, val, i) => {
acc.push( i>1 ? acc[i-1]+acc[i-2] : val);
@ -199,16 +180,37 @@ var fibonacci = n =>
},[]);
```
### Filter out non-unique values in an array
Use `Array.filter()` for an array containing only the unique values.
```js
const unique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));
// unique([1,2,2,3,4,4,5]) -> [1,3,5]
```
### Flatten array
Use recursion.
Use `reduce()` to get all elements that are not arrays, flatten each element that is an array.
```js
var flatten = arr =>
const flatten = arr =>
arr.reduce( (a, v) => a.concat( Array.isArray(v) ? flatten(v) : v ), []);
```
## Get scroll position
Use `pageXOffset` and `pageYOffset` if they are defined, otherwise `scrollLeft` and `scrollTop`.
You can omit `el` to use a default value of `window`.
```js
const getScrollPos = (el = window) =>
( {x: (el.pageXOffset !== undefined) ? el.pageXOffset : el.scrollLeft,
y: (el.pageYOffset !== undefined) ? el.pageYOffset : el.scrollTop} );
// getScrollPos() -> {x: 0, y: 200}
```
### Greatest common divisor (GCD)
Use recursion.
@ -216,7 +218,7 @@ Base case is when `y` equals `0`. In this case, return `x`.
Otherwise, return the GCD of `y` and the remainder of the division `x/y`.
```js
var gcd = (x , y) => !y ? x : gcd(y, x % y);
const gcd = (x , y) => !y ? x : gcd(y, x % y);
```
### Head of list
@ -224,7 +226,7 @@ var gcd = (x , y) => !y ? x : gcd(y, x % y);
Return `arr[0]`.
```js
var head = arr => arr[0];
const head = arr => arr[0];
```
### Initial of list
@ -232,7 +234,7 @@ var head = arr => arr[0];
Return `arr.slice(0,-1)`.
```js
var initial = arr => arr.slice(0,-1);
const initial = arr => arr.slice(0,-1);
```
### Initialize array with range
@ -241,7 +243,7 @@ Use `Array(end-start)` to create an array of the desired length, `map()` to fill
You can omit `start` to use a default value of `0`.
```js
var initializeArrayRange = (end, start = 0) =>
const initializeArrayRange = (end, start = 0) =>
Array.apply(null, Array(end-start)).map( (v,i) => i + start );
```
@ -251,7 +253,7 @@ Use `Array(n)` to create an array of the desired length, `fill(v)` to fill it wi
You can omit `v` to use a default value of `0`.
```js
var initializeArray = (n, v = 0) =>
const initializeArray = (n, v = 0) =>
Array(n).fill(v);
```
@ -260,7 +262,7 @@ var initializeArray = (n, v = 0) =>
Return `arr.slice(-1)[0]`.
```js
var initial = arr => arr.slice(-1)[0];
const last = arr => arr.slice(-1)[0];
```
### Measure time taken by function
@ -269,7 +271,7 @@ Use `performance.now()` to get start and end time for the function, `console.log
First argument is the function name, subsequent arguments are passed to the function.
```js
var timeTaken = (f,...args) => {
const timeTaken = (f,...args) => {
var t0 = performance.now(), r = f(...args);
console.log(performance.now() - t0);
return r;
@ -278,19 +280,18 @@ var timeTaken = (f,...args) => {
### Object from key-value pairs
Use `map()` to create objects for each key-value pair, combine with `Object.assign()`.
Use `Array.reduce()` to create and combine key-value pairs.
```js
var objectFromPairs = arr =>
Object.assign(...arr.map( v => ({ [v[0]] : v[1] })));
const objectFromPairs = arr => arr => arr.reduce((a,b) => { a[b[0]] = b[1]; return a;}, {});
```
### Powerset
Use `reduce()` combined with `map()` to iterate over elements and combine into an array containing all combinations.
Use `reduce()` combined with `map()` to iterate over elements and combine into an array containing all combinations.
```js
var powerset = arr =>
const powerset = arr =>
arr.reduce( (a,v) => a.concat(a.map( r => [v].concat(r) )), [[]]);
```
@ -299,7 +300,7 @@ var powerset = arr =>
Use `Math.random()` to generate a random value, map it to the desired range using multiplication.
```js
var randomInRange = (min, max) => Math.random() * (max - min) + min;
const randomInRange = (min, max) => Math.random() * (max - min) + min;
```
### Randomize order of array
@ -307,7 +308,7 @@ var randomInRange = (min, max) => Math.random() * (max - min) + min;
Use `sort()` to reorder elements, utilizing `Math.random()` to randomize the sorting.
```js
var randomizeOrder = arr => arr.sort( (a,b) => Math.random() >= 0.5 ? -1 : 1)
const randomizeOrder = arr => arr.sort( (a,b) => Math.random() >= 0.5 ? -1 : 1)
```
### Redirect to URL
@ -316,18 +317,37 @@ Use `window.location.href` or `window.location.replace()` to redirect to `url`.
Pass a second argument to simulate a link click (`true` - default) or an HTTP redirect (`false`).
```js
var redirect = (url, asLink = true) =>
const redirect = (url, asLink = true) =>
asLink ? window.location.href = url : window.location.replace(url);
```
### Reverse a string
Use array destructuring and `Array.reverse()` to reverse the order of the characters in the string.
Combine characters to get a string using `join('')`.
```js
const reverseString = str => [...str].reverse().join('');
```
### RGB to hexadecimal
Convert each value to a hexadecimal string, using `toString(16)`, then `padStart(2,'0')` to get a 2-digit hexadecimal value.
Combine values using `join('')`.
```js
const rgbToHex = (r, g, b) =>
[r,g,b].map( v => v.toString(16).padStart(2,'0')).join('');
```
### Scroll to top
Get distance from top using `document.documentElement.scrollTop` or `document.body.scrollTop`.
Scroll by a fraction of the distance from top. Use `window.requestFrame()` to animate the scrolling.
Scroll by a fraction of the distance from top. Use `window.requestAnimationFrame()` to animate the scrolling.
```js
var scrollToTop = _ => {
var c = document.documentElement.scrollTop || document.body.scrollTop;
const scrollToTop = _ => {
const c = document.documentElement.scrollTop || document.body.scrollTop;
if(c > 0) {
window.requestAnimationFrame(scrollToTop);
window.scrollTo(0, c - c/8);
@ -337,11 +357,10 @@ var scrollToTop = _ => {
### Similarity between arrays
Use `filter()` to remove values that are not part of `values`, determined using `indexOf()`.
Use `filter()` to remove values that are not part of `values`, determined using `includes()`.
```js
var difference = (arr, values) =>
arr.filter(v => values.indexOf(v) !== -1);
const difference = (arr, values) => arr.filter(v => values.includes(v));
```
### Sort characters in string (alphabetical)
@ -349,7 +368,7 @@ var difference = (arr, values) =>
Split the string using `split('')`, `sort()` utilizing `localeCompare()`, recombine using `join('')`.
```js
var sortCharactersInString = str =>
const sortCharactersInString = str =>
str.split('').sort( (a,b) => a.localeCompare(b) ).join('');
```
@ -358,7 +377,7 @@ var sortCharactersInString = str =>
Use `reduce()` to add each value to an accumulator, initialized with a value of `0`.
```js
var sum = arr =>
const sum = arr =>
arr.reduce( (acc , val) => acc + val, 0);
```
@ -375,21 +394,38 @@ Use array destructuring to swap values between two variables.
Return `arr.slice(1)`.
```js
var tail = arr => arr.slice(1);
const tail = arr => arr.slice(1);
```
### Unique values of array
Use `reduce()` to accumulate all unique values in an array.
Check if each value has already been added, using `indexOf()` on the accumulator array.
Use ES6 `Set` and the `...rest` operator to discard all duplicated values.
```js
var uniqueValues = arr =>
arr.reduce( (acc, val) => {
if(acc.indexOf(val) === -1)
acc.push(val);
return acc;
}, []);
const unique = arr => [...new Set(arr)];
// unique([1,2,2,3,4,4,5]) -> [1,2,3,4,5]
```
### URL parameters
Use `match()` with an appropriate regular expression to get all key-value pairs, `map()` them appropriately.
Combine all key-value pairs into a single object using `Object.assign()` and the spread operator (`...`).
Pass `location.search` as the argument to apply to the current `url`.
```js
const getUrlParameters = url =>
Object.assign(...url.match(/([^?=&]+)(=([^&]*))?/g).map(m => {[f,v] = m.split('='); return {[f]:v}}));
```
### UUID generator
Use `crypto` API to generate a UUID, compliant with [RFC4122](https://www.ietf.org/rfc/rfc4122.txt) version 4.
```js
const uuid = _ =>
( [1e7]+-1e3+-4e3+-8e3+-1e11 ).replace( /[018]/g, c =>
(c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> c / 4).toString(16)
)
```
### Validate number
@ -398,7 +434,7 @@ Use `!isNaN` in combination with `parseFloat()` to check if the argument is a nu
Use `isFinite()` to check if the number is finite.
```js
var validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n);
const validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n);
```
## Credits

14
scripts/builder.js
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@ -7,7 +7,19 @@ var staticPartsPath = './static-parts';
var snippets = {}, startPart = '', endPart = '', output = '';
try {
for(var snippet of fs.readdirSync(snippetsPath)){
var snippetFilenames = fs.readdirSync(snippetsPath);
snippetFilenames.sort((a, b) => {
a = a.toLowerCase();
b = b.toLowerCase();
if (a < b) {
return -1;
}
if (a > b) {
return 1;
}
return 0;
});
for(var snippet of snippetFilenames){
snippets[snippet] = fs.readFileSync(path.join(snippetsPath,snippet),'utf8');
}
}

2
snippets/RGB-to-hexadecimal.md
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@ -4,6 +4,6 @@ Convert each value to a hexadecimal string, using `toString(16)`, then `padStart
Combine values using `join('')`.
```js
var rgbToHex = (r, g, b) =>
const rgbToHex = (r, g, b) =>
[r,g,b].map( v => v.toString(16).padStart(2,'0')).join('');
```

2
snippets/URL-parameters.md
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@ -5,6 +5,6 @@ Combine all key-value pairs into a single object using `Object.assign()` and the
Pass `location.search` as the argument to apply to the current `url`.
```js
var getUrlParameters = url =>
const getUrlParameters = url =>
Object.assign(...url.match(/([^?=&]+)(=([^&]*))?/g).map(m => {[f,v] = m.split('='); return {[f]:v}}));
```

2
snippets/UUID-generator.md
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@ -3,7 +3,7 @@
Use `crypto` API to generate a UUID, compliant with [RFC4122](https://www.ietf.org/rfc/rfc4122.txt) version 4.
```js
var uuid = _ =>
const uuid = _ =>
( [1e7]+-1e3+-4e3+-8e3+-1e11 ).replace( /[018]/g, c =>
(c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> c / 4).toString(16)
)

2
snippets/anagrams-of-string-(with-duplicates).md
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@ -6,7 +6,7 @@ Use `map()` to combine the letter with each partial anagram, then `reduce()` to
Base cases are for string `length` equal to `2` or `1`.
```js
var anagrams = s => {
const anagrams = s => {
if(s.length <= 2) return s.length === 2 ? [s, s[1] + s[0]] : [s];
return s.split('').reduce( (a,l,i) => {
anagrams(s.slice(0,i) + s.slice(i+1)).map( v => a.push(l+v) );

2
snippets/average-of-array-of-numbers.md
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@ -3,6 +3,6 @@
Use `reduce()` to add each value to an accumulator, initialized with a value of `0`, divide by the `length` of the array.
```js
var average = arr =>
const average = arr =>
arr.reduce( (acc , val) => acc + val, 0) / arr.length;
```

7
snippets/capitalize-first-letter-of-every-word.md Normal file
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@ -0,0 +1,7 @@
### Capitalize first letter of every word
Use `replace()` to match the first character of each word and `toUpperCase()` to capitalize it.
```js
const capitalizeEveryWord = str => str.replace(/\b[a-z]/g, char => char.toUpperCase());
```

6
snippets/capitalize-first-letter.md
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@ -1,7 +1,9 @@
### Capitalize first letter
Use `toUpperCase()` to capitalize first letter, `slice(1)` to get the rest of the string.
Use `slice(0,1)` and `toUpperCase()` to capitalize first letter, `slice(1)` to get the rest of the string.
Omit the `lowerRest` parameter to keep the rest of the string intact, or set it to `true` to convert to lower case.
```js
var capitalize = str => str[0].toUpperCase() + str.slice(1);
const capitalize = (str, lowerRest = false) =>
str.slice(0, 1).toUpperCase() + (lowerRest? str.slice(1).toLowerCase() : str.slice(1));
```

4
snippets/count-occurrences-of-a-value-in-array.md
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@ -1,7 +1,7 @@
### Count occurrences of a value in array
Use `filter()` to create an array containing only the items with the specified value, count them using `length`.
Use `reduce()` to increment a counter each time you encounter the specific value inside the array.
```js
var countOccurrences = (arr, value) => arr.filter(v => v === value).length;
const countOccurrences = (arr, value) => arr.reduce((a, v) => v===value ? a + 1 : a + 0, 0);
```

2
snippets/current-URL.md
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@ -3,5 +3,5 @@
Use `window.location.href` to get current URL.
```js
var currentUrl = _ => window.location.href;
const currentUrl = _ => window.location.href;
```

2
snippets/curry.md
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@ -5,7 +5,7 @@ If the number of provided arguments (`args`) is sufficient, call the passed func
Otherwise return a curried function `f` that expects the rest of the arguments.
```js
var curry = f =>
const curry = f =>
(...args) =>
args.length >= f.length ? f(...args) : (...otherArgs) => curry(f)(...args, ...otherArgs)
```

5
snippets/difference-between-arrays.md
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@ -1,8 +1,7 @@
### Difference between arrays
Use `filter()` to remove values that are part of `values`, determined using `indexOf()`.
Use `filter()` to remove values that are part of `values`, determined using `includes()`.
```js
var difference = (arr, values) =>
arr.filter(v => values.indexOf(v) === -1);
const difference = (arr, values) => arr.filter(v => !values.includes(v));
```

5
snippets/distance-between-two-points.md
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@ -1,8 +1,7 @@
### Distance between two points
Use `Math.pow()` and `Math.sqrt()` to calculate the Euclidean distance between two points.
Use `Math.hypot()` to calculate the Euclidean distance between two points.
```js
var distance = x0, y0, x1, y1 =>
Math.sqrt(Math.pow(x1-x0, 2) + Math.pow(y1 - y0, 2))
const distance = (x0, y0, x1, y1) => Math.hypot(x1 - x0, y1 - y0);
```

2
snippets/escape-regular-expression.md
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@ -3,7 +3,7 @@
Use `replace()` to escape special characters.
```js
var escapeRegExp = s =>
const escapeRegExp = s =>
s.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
}
```

2
snippets/even-or-odd-number.md
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@ -4,5 +4,5 @@ Use `Math.abs()` to extend logic to negative numbers, check using the modulo (`%
Return `true` if the number is even, `false` if the number is odd.
```js
var isEven = num => Math.abs(num) % 2 === 0;
const isEven = num => Math.abs(num) % 2 === 0;
```

7
snippets/factorial.md
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@ -1,8 +1,9 @@
### Factorial
Create an array of length `n+1`, use `reduce()` to get the product of every value in the given range, utilizing the index of each element.
Use recursion.
If `n` is less than or equal to `1`, return `1`.
Otherwise, return the product of `n` and the factorial of `n - 1`.
```js
var factorial = n =>
Array.apply(null, [1].concat(Array(n))).reduce( (a, _, i) => a * i || 1 , 1);
const factorial = n => n <= 1 ? 1 : n * factorial(n - 1)
```

2
snippets/fibonacci-array-generator.md
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@ -4,7 +4,7 @@ Create an empty array of the specific length, initializing the first two values
Use `reduce()` to add values into the array, using the sum of the last two values, except for the first two.
```js
var fibonacci = n =>
const fibonacci = n =>
Array.apply(null, [0,1].concat(Array(n-2))).reduce(
(acc, val, i) => {
acc.push( i>1 ? acc[i-1]+acc[i-2] : val);

8
snippets/filter-out-non-uniqe-values-in-an-array.md Normal file
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@ -0,0 +1,8 @@
### Filter out non-unique values in an array
Use `Array.filter()` for an array containing only the unique values.
```js
const unique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));
// unique([1,2,2,3,4,4,5]) -> [1,3,5]
```

2
snippets/flatten-array.md
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@ -4,6 +4,6 @@ Use recursion.
Use `reduce()` to get all elements that are not arrays, flatten each element that is an array.
```js
var flatten = arr =>
const flatten = arr =>
arr.reduce( (a, v) => a.concat( Array.isArray(v) ? flatten(v) : v ), []);
```

11
snippets/get-scroll-position.md Normal file
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@ -0,0 +1,11 @@
## Get scroll position
Use `pageXOffset` and `pageYOffset` if they are defined, otherwise `scrollLeft` and `scrollTop`.
You can omit `el` to use a default value of `window`.
```js
const getScrollPos = (el = window) =>
( {x: (el.pageXOffset !== undefined) ? el.pageXOffset : el.scrollLeft,
y: (el.pageYOffset !== undefined) ? el.pageYOffset : el.scrollTop} );
// getScrollPos() -> {x: 0, y: 200}
```

2
snippets/greatest-common-divisor-(GCD).md
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@ -5,5 +5,5 @@ Base case is when `y` equals `0`. In this case, return `x`.
Otherwise, return the GCD of `y` and the remainder of the division `x/y`.
```js
var gcd = (x , y) => !y ? x : gcd(y, x % y);
const gcd = (x , y) => !y ? x : gcd(y, x % y);
```

2
snippets/head-of-list.md
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@ -3,5 +3,5 @@
Return `arr[0]`.
```js
var head = arr => arr[0];
const head = arr => arr[0];
```

2
snippets/initial-of-list.md
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@ -3,5 +3,5 @@
Return `arr.slice(0,-1)`.
```js
var initial = arr => arr.slice(0,-1);
const initial = arr => arr.slice(0,-1);
```

2
snippets/initialize-array-with-range.md
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@ -4,6 +4,6 @@ Use `Array(end-start)` to create an array of the desired length, `map()` to fill
You can omit `start` to use a default value of `0`.
```js
var initializeArrayRange = (end, start = 0) =>
const initializeArrayRange = (end, start = 0) =>
Array.apply(null, Array(end-start)).map( (v,i) => i + start );
```

2
snippets/initialize-array-with-values.md
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@ -4,6 +4,6 @@ Use `Array(n)` to create an array of the desired length, `fill(v)` to fill it wi
You can omit `v` to use a default value of `0`.
```js
var initializeArray = (n, v = 0) =>
const initializeArray = (n, v = 0) =>
Array(n).fill(v);
```

2
snippets/last-of-list.md
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@ -3,5 +3,5 @@
Return `arr.slice(-1)[0]`.
```js
var initial = arr => arr.slice(-1)[0];
const last = arr => arr.slice(-1)[0];
```

2
snippets/measure-time-taken-by-function.md
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@ -4,7 +4,7 @@ Use `performance.now()` to get start and end time for the function, `console.log
First argument is the function name, subsequent arguments are passed to the function.
```js
var timeTaken = (f,...args) => {
const timeTaken = (f,...args) => {
var t0 = performance.now(), r = f(...args);
console.log(performance.now() - t0);
return r;

2
snippets/object-from-key-value-pairs.md
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@ -3,5 +3,5 @@
Use `Array.reduce()` to create and combine key-value pairs.
```js
const objectFromPairs = arr => arr => arr.reduce((a,b) => { a[b[0]] = b[1]; return a;}, {})
const objectFromPairs = arr => arr => arr.reduce((a,b) => { a[b[0]] = b[1]; return a;}, {});
```

4
snippets/powerset.md
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@ -1,8 +1,8 @@
### Powerset
Use `reduce()` combined with `map()` to iterate over elements and combine into an array containing all combinations.
Use `reduce()` combined with `map()` to iterate over elements and combine into an array containing all combinations.
```js
var powerset = arr =>
const powerset = arr =>
arr.reduce( (a,v) => a.concat(a.map( r => [v].concat(r) )), [[]]);
```

2
snippets/random-number-in-range.md
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@ -3,5 +3,5 @@
Use `Math.random()` to generate a random value, map it to the desired range using multiplication.
```js
var randomInRange = (min, max) => Math.random() * (max - min) + min;
const randomInRange = (min, max) => Math.random() * (max - min) + min;
```

2
snippets/randomize-order-of-array.md
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@ -3,5 +3,5 @@
Use `sort()` to reorder elements, utilizing `Math.random()` to randomize the sorting.
```js
var randomizeOrder = arr => arr.sort( (a,b) => Math.random() >= 0.5 ? -1 : 1)
const randomizeOrder = arr => arr.sort( (a,b) => Math.random() >= 0.5 ? -1 : 1)
```

2
snippets/redirect-to-url.md
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@ -4,6 +4,6 @@ Use `window.location.href` or `window.location.replace()` to redirect to `url`.
Pass a second argument to simulate a link click (`true` - default) or an HTTP redirect (`false`).
```js
var redirect = (url, asLink = true) =>
const redirect = (url, asLink = true) =>
asLink ? window.location.href = url : window.location.replace(url);
```

8
snippets/reverse-a-string.md Normal file
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@ -0,0 +1,8 @@
### Reverse a string
Use array destructuring and `Array.reverse()` to reverse the order of the characters in the string.
Combine characters to get a string using `join('')`.
```js
const reverseString = str => [...str].reverse().join('');
```

6
snippets/scroll-to-top.md
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@ -1,11 +1,11 @@
### Scroll to top
Get distance from top using `document.documentElement.scrollTop` or `document.body.scrollTop`.
Scroll by a fraction of the distance from top. Use `window.requestFrame()` to animate the scrolling.
Scroll by a fraction of the distance from top. Use `window.requestAnimationFrame()` to animate the scrolling.
```js
var scrollToTop = _ => {
var c = document.documentElement.scrollTop || document.body.scrollTop;
const scrollToTop = _ => {
const c = document.documentElement.scrollTop || document.body.scrollTop;
if(c > 0) {
window.requestAnimationFrame(scrollToTop);
window.scrollTo(0, c - c/8);

5
snippets/similarity-between-arrays.md
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@ -1,8 +1,7 @@
### Similarity between arrays
Use `filter()` to remove values that are not part of `values`, determined using `indexOf()`.
Use `filter()` to remove values that are not part of `values`, determined using `includes()`.
```js
var difference = (arr, values) =>
arr.filter(v => values.indexOf(v) !== -1);
const difference = (arr, values) => arr.filter(v => values.includes(v));
```

2
snippets/sort-characters-in-string-(alphabetical).md
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@ -3,6 +3,6 @@
Split the string using `split('')`, `sort()` utilizing `localeCompare()`, recombine using `join('')`.
```js
var sortCharactersInString = str =>
const sortCharactersInString = str =>
str.split('').sort( (a,b) => a.localeCompare(b) ).join('');
```

2
snippets/sum-of-array-of-numbers.md
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@ -3,6 +3,6 @@
Use `reduce()` to add each value to an accumulator, initialized with a value of `0`.
```js
var sum = arr =>
const sum = arr =>
arr.reduce( (acc , val) => acc + val, 0);
```

2
snippets/tail-of-list.md
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@ -3,5 +3,5 @@
Return `arr.slice(1)`.
```js
var tail = arr => arr.slice(1);
const tail = arr => arr.slice(1);
```

11
snippets/unique-values-of-array.md
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@ -1,13 +1,8 @@
### Unique values of array
Use `reduce()` to accumulate all unique values in an array.
Check if each value has already been added, using `indexOf()` on the accumulator array.
Use ES6 `Set` and the `...rest` operator to discard all duplicated values.
```js
var uniqueValues = arr =>
arr.reduce( (acc, val) => {
if(acc.indexOf(val) === -1)
acc.push(val);
return acc;
}, []);
const unique = arr => [...new Set(arr)];
// unique([1,2,2,3,4,4,5]) -> [1,2,3,4,5]
```

2
snippets/validate-number.md
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@ -4,5 +4,5 @@ Use `!isNaN` in combination with `parseFloat()` to check if the argument is a nu
Use `isFinite()` to check if the number is finite.
```js
var validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n);
const validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n);
```