# 30 seconds of code
> Curated collection of useful Javascript snippets that you can understand in 30 seconds or less.
- Use Ctrl + F or command + F to search for a snippet.
- Contributions welcome, please read [contribution guide](contributing.md).
## Contents
* [Even or odd number](#even-or-odd-number)
* [Fibonacci array generator](#fibonacci-array-generator)
* [Greatest common divisor (GCD)](#greatest-common-divisor-gcd)
* [Initialize array with values](#initialize-array-with-values)
* [Random number in range](#random-number-in-range)
* [Randomize order of array](#randomize-order-of-array)
* [RGB to hexadecimal](#rgb-to-hexadecimal)
* [Sort characters in string alphabetical](#sort-characters-in-string-alphabetical)
* [Sum of array of numbers](#sum-of-array-of-numbers)
* [Unique values of array](#unique-values-of-array)
### Even or odd number
Use `Math.abs()` to extend logic to negative numbers, check using the modulo (`%`) operator.
Return `true` if the number is even, `false` if the number is odd.
```js
var isEven = num => Math.abs(num) % 2 === 0;
```
### Fibonacci array generator
Create an empty array of the specific length, initializing the first two values (`0` and `1`).
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 =>
Array.apply(null, [0,1].concat(Array(n-2))).reduce(
(acc, val, i) => {
acc.push( i>1 ? acc[i-1]+acc[i-2] : val);
return acc;
},[]);
```
### Greatest common divisor (GCD)
Use recursion.
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);
```
### Initialize array with values
Use `Array(n)` to create an array of the desired length, `fill(v)` to fill it with the desired values.
You can omit `v` to use a default value of `0`.
```js
var initializeArray = (n, v = 0) =>
Array(n).fill(v);
```
### Random number in range
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;
```
### Randomize order of array
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)
```
### 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('');
```
### Sort characters in string (alphabetical)
Split the string using `split('')`, `sort()` utilizing `localeCompare()`, recombine using `join('')`.
```js
var sortCharactersInString = str =>
str.split('').sort( (a,b) => a.localeCompare(b) ).join('');
```
### Sum of array of numbers
Use `reduce()` to add each value to an accumulator, initialized with a value of `0`.
```js
var sum = arr =>
arr.reduce( (acc , val) => acc + val, 0);
```
### 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.
```js
var uniqueValues = arr =>
arr.reduce( (acc, val) => {
if(acc.indexOf(val) === -1)
acc.push(val);
return acc;
}, []);
```
## Credits
*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/).*