6.4 Array Methods

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

• 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.

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

const arr = [NaN];
alert( arr.indexOf(NaN) ); // -1 (should be 0, but === equality doesn't work for NaN)
alert( arr.includes(NaN) );// true (correct)

find and findIndex

let result = arr.find(function(item, index, array) {
  // if true is returned, item is returned and iteration is stopped
  // for falsy scenario returns undefined
});

• item is the element.

• index is its index.

• array is the array itself.

let users = [
  {id: 1, name: "John"},
  {id: 2, name: "Pete"},
  {id: 3, name: "Mary"}
];

let user = users.find(item => item.id == 1);

alert(user.name); // John