JavaScript Array Methods
Tags: javascript, programming
Published: 2022-05-12 00:34:33

## Array Mutation Methods
Changes original array

- `pop()`: Removes the las element of an array and returns it.
```javascript
const array = ['Element 1', 'Element 2', 'Element 3'];
console.log(array.pop()); // 'Element 3'
console.log(array); // ['Element 1', 'Element 2'];
```

- `shift()`: Removes the firts element of an array and returns it.
```javascript
const array = ['Element 1', 'Element 2', 'Element 3'];
console.log(array.shift()); // 'Element 1'
console.log(array); // ['Element 2', 'Element 3'];
```

- `push()`: Adds a new element to the array, at the end of the array, and returns the new length of the array.
```javascript
const array = ['Element 1', 'Element 2', 'Element 3'];
console.log(array.push('Element 4')); // 4
console.log(array); // [ 'Element 1', 'Element 2', 'Element 3', 'Element 4' ]
```

- `reverse()`: Reverses the order of the elements in an array.
```javascript
const array = ['Element 1', 'Element 2', 'Element 3'];
console.log(array.reverse()); // [ 'Element 3', 'Element 2', 'Element 1' ]
console.log(array); // [ 'Element 3', 'Element 2', 'Element 1' ]
```

- `unshift()`: Adds one or more elements to the beginning of an array, and returns the new length of the array.
```javascript
const array = ['Element 1', 'Element 2', 'Element 3'];
console.log(array.unshift('Element 4')); // 4
console.log(array); // [ 'Element 4', 'Element 1', 'Element 2', 'Element 3' ]
```

- `sort()`: Sorts the elements of an array.
```javascript
const array = [2, 8, 1, 4];
console.log(array.sort()); // [ 1, 2, 4, 8 ]
console.log(array); // [ 1, 2, 4, 8 ]
```

- `splice()`: Changes the contents of an array, removing existing elements and/or adds new elements.
```javascript
const array = [2, 8, 1, 4, 'a', 'b'];
console.log(array.splice(1,3,'a')); // [ 8, 1, 4 ]
console.log(array); // [ 2, 'a', 'a', 'b' ]
```

## Array Accessor Methods
Does not modify the original array. Creates new array.

- `join()`: Joins all the elements of an array into a string and returns the string.
```javascript
const array = [2, 8, 1, 4, 'a', 'b', 'c'];

console.log(array.join()); // '2,8,1,4,a,b,c'
console.log(array); // [ 2, 8, 1, 4, 'a', 'b', 'c' ]
```

- `slice()`: Returns a part of the array in a new array.
```javascript
const array = ['Element 1', 'Element 2', 'Element 3'];

console.log(array.slice(1, 2)); // [ 'Element 2' ]
console.log(array); // [ 'Element 1', 'Element 2', 'Element 3' ]
```

- `concat()`: Joins two or more arrays into one.
```javascript
const array = ['Element 1', 'Element 2', 'Element 3'];
const array2 = [1, 2, 3];
const array3 = [true, false];

console.log(array.concat(array2, array3)); // [ 'Element 1', 'Element 2', 'Element 3', 1, 2, 3, true, false ]
console.log(array); // [ 'Element 1', 'Element 2', 'Element 3' ]
```

- `includes()`: Returns true if it finds the string, number, etc. or returns false if it finds nothing.
```javascript
const array = ['Element 1', 'Element 2', 'Element 3'];

console.log(array.includes(2)); // false
console.log(array.includes('Element 1')); // true
```

- `toString()`: Returns all elements of the array, in a string.
```javascript
const array = ['Element 1', 'Element 2', 'Element 3'];

console.log(array.toString()); // 'Element 1,Element 2,Element 3'
```

- `indexOf()`: Returns the first index that matches the search.
```javascript
const array = [1, 2, 3, 4, 1, 3, 5, 2, 1];

console.log(array.indexOf(1)); // 0
```

- `lastIndexOf()`: Returns the last index that matches the search.
```javascript
const array = [1, 2, 3, 4, 1, 3, 5, 2, 1];

console.log(array.lastIndexOf(2)); // 7
```