push()
ES3+Adds one or more elements to the end of an array and returns the new length.
Syntax
array.push(element1, element2, ...)Parameters
elements any Elements to add to the end of the array
Return Value
The new length of the array
Examples
const fruits = ['apple', 'banana'];
const newLength = fruits.push('cherry');
console.log(fruits);
console.log(newLength);📌 When to Use
Use push() when you need to add elements to the end of an array. It's the most common way to build arrays incrementally, implement queues, or collect results from loops.
⚠️ Common Mistakes
Using arr.push([...items]) instead of arr.push(...items) - creates nested array
Expecting push() to return the modified array - it returns the new length
Using push() in React/Vue state directly - use spread instead: [...state, newItem]
✅ Best Practices
For immutable operations, use spread: const newArr = [...arr, newItem]
Push multiple items at once: arr.push(item1, item2, item3) is more efficient
Use push with spread to add array items: arr.push(...otherArr)
⚡ Performance Notes
push() is O(1) amortized - very fast for adding to the end. JavaScript arrays are dynamic, so occasional resizing may occur. For building large arrays, push() is much faster than using concat() or spread in a loop.
🌍 Real World Example
Collecting Form Validation Errors
Build an array of validation errors while checking form fields
function validateForm(data) {
const errors = [];
if (!data.email) {
errors.push('Email is required');
} else if (!data.email.includes('@')) {
errors.push('Invalid email format');
}
if (!data.password) {
errors.push('Password is required');
} else if (data.password.length < 8) {
errors.push('Password must be at least 8 characters');
}
return errors; // ['Invalid email format', 'Password must be at least 8 characters']
}