let tasks = ["study", "gym"];
let newLength = tasks.push("sleep");
console.log(tasks);     // ["study", "gym", "sleep"]
console.log(newLength); // 3

tasks.push("cook", "read");
console.log(tasks); // ["study", "gym", "sleep", "cook", "read"]

Removes the last item: and gives it back to you.

Changes the original array: the array gets one item shorter.

Returns the removed item: handy when you want to use it.

Takes no arguments: you just call it.

let fruits = ["apple", "banana", "mango"];
let removed = fruits.pop();
console.log(removed); // "mango"
console.log(fruits);  // ["apple", "banana"]

console.log([].pop()); // undefined

array.push(item1, item2, ...);
array.pop();

Building a list as you go:

let evens = [];
for (let i = 1; i <= 10; i++) {
  if (i % 2 === 0) {
    evens.push(i);
  }
}
console.log(evens); // [2, 4, 6, 8, 10]

Undo history: pop the last action off.

let actions = ["type", "bold", "delete"];
let undone = actions.pop();
console.log(undone);  // "delete"
console.log(actions); // ["type", "bold"]

Adding objects to a list:

let users = [];
users.push({ name: "Vi", age: 22 });
users.push({ name: "Sam", age: 30 });
console.log(users.length); // 2

Reversing a string with a stack:

let text = "hello";
let stack = [];
for (let char of text) {
  stack.push(char);
}
let reversed = "";
while (stack.length > 0) {
  reversed += stack.pop();
}
console.log(reversed); // "olleh"

Using Them Together as a Stack

Last in, first out: the last item you push is the first one you pop.

let stack = [];
stack.push("a");
stack.push("b");
stack.push("c");
console.log(stack.pop()); // "c"
console.log(stack.pop()); // "b"
console.log(stack);       // ["a"]

Where it's used: undo features, the browser's back button, checking matching brackets, and function call tracking.
 

Things to Remember

Both change the original array: copy it first if you need to keep the original.

let original = [1, 2, 3];
let copy = [...original];
copy.push(4);
console.log(original); // [1, 2, 3]
console.log(copy);     // [1, 2, 3, 4]

push() with an array adds it as one item: it doesn't merge the items in.

let a = [1, 2];
a.push([3, 4]);
console.log(a); // [1, 2, [3, 4]]
let b = [1, 2];
b.push(...[3, 4]);
console.log(b); // [1, 2, 3, 4]

They're fast: working at the end of an array doesn't force other items to move, unlike shift() and unshift().
 

Common Mistakes

Expecting push() to return the array: it returns the new length, so you can't chain it.

let result = [1, 2].push(3);
console.log(result); // 3, not an array

Pushing an array when you meant to merge: use the spread operator or concat() instead.

Forgetting that they change the original: this causes bugs when the same array is used elsewhere.
 

Conclusion

Frequently Asked Questions (FAQs)

The new length of the array, not the array itself.

2.What happens if I call pop() on an empty array?

It returns undefined and doesn't throw an error.

3. How do I add or remove from the start of an array?

Use unshift() to add and shift() to remove.