127 lines
3.6 KiB
Markdown
127 lines
3.6 KiB
Markdown
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# 30 seconds of code
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> Curated collection of useful Javascript snippets that you can understand in 30 seconds or less.
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- Use <kbd>Ctrl</kbd> + <kbd>F</kbd> or <kbd>command</kbd> + <kbd>F</kbd> to search for a snippet.
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- Contributions welcome, please read [contribution guide](contributing.md).
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## Contents
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* [Even or odd number](#even-or-odd-number)
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* [Fibonacci array generator](#fibonacci-array-generator)
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* [Greatest common divisor (GCD)](#greatest-common-divisor-gcd)
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* [Initialize array with values](#initialize-array-with-values)
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* [Random number in range](#random-number-in-range)
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* [Randomize order of array](#randomize-order-of-array)
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* [RGB to hexadecimal](#rgb-to-hexadecimal)
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* [Sort characters in string alphabetical](#sort-characters-in-string-alphabetical)
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* [Sum of array of numbers](#sum-of-array-of-numbers)
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* [Unique values of array](#unique-values-of-array)
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### Even or odd number
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Use `Math.abs()` to extend logic to negative numbers, check using the modulo (`%`) operator.
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Return `true` if the number is even, `false` if the number is odd.
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```js
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var isEven = num => Math.abs(num) % 2 === 0;
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```
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### Fibonacci array generator
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Create an empty array of the specific length, initializing the first two values (`0` and `1`).
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Use `reduce()` to add values into the array, using the sum of the last two values, except for the first two.
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```js
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var fibonacci = n =>
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Array.apply(null, [0,1].concat(Array(n-2))).reduce(
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(acc, val, i) => {
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acc.push( i>1 ? acc[i-1]+acc[i-2] : val);
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return acc;
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},[]);
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```
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### Greatest common divisor (GCD)
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Use recursion.
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Base case is when `y` equals `0`. In this case, return `x`.
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Otherwise, return the GCD of `y` and the remainder of the division `x/y`.
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```js
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var gcd = (x , y) => !y ? x : gcd(y, x % y);
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```
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### Initialize array with values
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Use `Array(n)` to create an array of the desired length, `fill(v)` to fill it with the desired values.
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You can omit `v` to use a default value of `0`.
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```js
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var initializeArray = (n, v = 0) =>
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Array(n).fill(v);
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```
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### Random number in range
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Use `Math.random()` to generate a random value, map it to the desired range using multiplication.
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```js
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var randomInRange = (min, max) => Math.random() * (max - min) + min;
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```
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### Randomize order of array
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Use `sort()` to reorder elements, utilizing `Math.random()` to randomize the sorting.
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```js
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var randomizeOrder = arr => arr.sort( (a,b) => Math.random() >= 0.5 ? -1 : 1)
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```
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### RGB to hexadecimal
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Convert each value to a hexadecimal string, using `toString(16)`, then `padStart(2,'0')` to get a 2-digit hexadecimal value.
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Combine values using `join('')`.
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```js
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var rgbToHex = (r, g, b) =>
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[r,g,b].map( v => v.toString(16).padStart(2,'0')).join('');
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```
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### Sort characters in string (alphabetical)
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Split the string using `split('')`, `sort()` utilizing `localeCompare()`, recombine using `join('')`.
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```js
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var sortCharactersInString = str =>
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str.split('').sort( (a,b) => a.localeCompare(b) ).join('');
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```
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### Sum of array of numbers
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Use `reduce()` to add each value to an accumulator, initialized with a value of `0`.
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```js
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var sum = arr =>
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arr.reduce( (acc , val) => acc + val, 0);
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```
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### Unique values of array
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Use `reduce()` to accumulate all unique values in an array.
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Check if each value has already been added, using `indexOf()` on the accumulator array.
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```js
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var uniqueValues = arr =>
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arr.reduce( (acc, val) => {
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if(acc.indexOf(val) === -1)
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acc.push(val);
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return acc;
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}, []);
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```
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## Credits
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*Icons made by [Smashicons](https://www.flaticon.com/authors/smashicons) from [www.flaticon.com](https://www.flaticon.com/) is licensed by [CC 3.0 BY](http://creativecommons.org/licenses/by/3.0/).*
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