introduction.md

In JavaScript, an array is a list-like structure with no fixed length which can hold any type of primitives or objects, or even mixed types. The array elements can be accessed by their index. Arrays are also given a bunch of built-in methods. Some of these built-in methods can analyse the contents of the array. Many of the built-in functions that analyse the contents of an array, take a predicate as argument.

The built-in functions are meant to be used instead of a for loop or the built-in Array#forEach():

Example of analysis using a for loop :

const numbers = [1, 'two', 3, 'four']
for (var i = 0; i < numbers.length; i++) {
    if (numbers[i] === 'two'){
        return numbers.[i]
    }
}
// => 1

Example of analysis using a built-in method:

const numbers = [1, 'two', 3, 'four']
numbers.indexOf('two')
// => 1