6.4 Array Methods

Add/Remove Items

• arr.push(...items) - adds items to the end.
• arr.pop() - extracts an item from the end.
• arr.shift() - extracts an item from the beginning.
• arr.filter(function(currentValue, index, arr), thisValue) - returns array that filtered out items that don't return true for the function.
  • thisValue is optional. A value to be passed to the function to be used as its "this" value.
• arr.unshift(...items) - adds items to the beginning.

Searching In A Array

indexOf/lastIndexOf and includes:

• arr.indexOf(item,from) - looks for item starting from index from , and returns the index where it was found, otherwise -1.
• arr.lastIndexOf(item, from) - same, but looks from right to left.

arr.includes(item, from) - looks for item starting from index from, returns true if found.

Example

let arr = [1, 0, false];

alert( arr.indexOf(0) ); // 1
alert( arr.indexOf(false) ); // 2
alert( arr.indexOf(null) ); // -1
alert( arr.includes(1) ); // true

<aside> 💡 Note that the methods use === comparison. So, if we look for false, it finds exactly false and not zero.

</aside>

If we want to check for inclusion, and don’t want to know the exact index, then arr.includes() is preferred.

Also, a very minor difference of includes is that it correctly handles NaN, unlike indexOf/lastIndexOf: