# Array Methods: push, pop, slice, splice — JavaScript

Source: https://www.geekswithgeeks.com/en/javascript/js-array-methods

> Adding, removing, and copying parts of an array.

## Adding & removing

`push`/`pop` work at the end, `unshift`/`shift` at the start — all four mutate the original array.

```js
const nums = [1, 2, 3];
nums.push(4);       // [1, 2, 3, 4]
nums.pop();          // removes 4 -> [1, 2, 3]
nums.unshift(0);     // [0, 1, 2, 3]
nums.shift();        // removes 0 -> [1, 2, 3]
```

## slice vs splice

`slice` copies a range without mutating; `splice` mutates the original array in place.

```js
const arr = [1, 2, 3, 4, 5];
console.log(arr.slice(1, 3));   // [2, 3], arr unchanged
arr.splice(1, 2, "a", "b");     // remove 2, insert 2
console.log(arr);               // [1, 'a', 'b', 4, 5]
```

## Mutating vs non-mutating

`push`, `pop`, `splice`, `sort`, `reverse` mutate. `slice`, `concat`, `map`, `filter` return a new array — know which is which.