What does push() do?
The push() method is one of the most frequently used in JavaScript.
It adds one or more elements to the end of an array
and returns the new length of the array.
Example:
javascript
const fruits = ["apple", "banana"];
const newLength = fruits.push("cherry");
console.log(fruits); // ["apple", "banana", "cherry"]
console.log(newLength); // 3- The method modifies the original array (mutates it).
- It returns not the array itself, but the number of elements after adding.
You can add several elements at once:
javascript
const arr = [1, 2];
arr.push(3, 4, 5);
console.log(arr); // [1, 2, 3, 4, 5]Behavior:
- Elements are added to the end of the array.
- The indexes of the new elements start at the current
length. - The return value is the new value of
arr.length.
Important:
-
push()only works with arrays (or array-like objects). -
If you do
arr = arr.push(...), you lose the array itself:javascriptconst arr = [1, 2]; arr = arr.push(3); // mistake - arr becomes a number (3)
In short:
| What it does | Adds elements to the end of the array |
|---|---|
| Modifies the original array? | Yes |
| Returns | The new length of the array |
| Can add several elements | Yes |
| Example | arr.push(1, 2, 3) |
Alternative (without mutation):
If you want to add an element without changing the original:
javascript
const arr = [1, 2];
const newArr = [...arr, 3];
console.log(newArr); // [1, 2, 3]
console.log(arr); // [1, 2] (unchanged)Short Answer
Interview readyPremium
A concise answer to help you respond confidently on this topic during an interview.