Sorting & Iteration

Sorting Arrays

• sort(): Sorts an array alphabetically.
• reverse(): Reverses the elements in an array.

Numeric Sort

By default, the sort() function sorts values as strings (so "25" is bigger than "100" because "2" > "1"). To sort numbers correctly:

const points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return a - b});

Array Iteration (High Order Functions)

1. forEach()

Calls a function once for each array element.

const numbers = [45, 4, 9, 16, 25];
numbers.forEach(myFunction);

function myFunction(value) {
  console.log(value);
}

2. map()

Creates a new array by performing a function on each array element.

const numbers1 = [45, 4, 9, 16, 25];
const numbers2 = numbers1.map(value => value * 2);

3. filter()

Creates a new array with all array elements that pass a test.

const over18 = numbers.filter(value => value > 18);

4. reduce()

Runs a function on each array element to produce (reduce it to) a single value.

let sum = numbers.reduce((total, value) => total + value);

Industry Standard

In React and modern JS development, map() and filter() are used constantly to render lists and manage data.