Arrays: Push, Pop, Shift, and Unshift
Like most variables in a program, you want to be able to alter their values. For primitive variables, like strings and numbers, you can only replace values. In a list like an array, you can add more items to it or take things away.
Adding to and removing from an array
There are a couple of ways to do this.
Push and Pop:
A pair of array methods .push(item) and .pop() are commonly used.
push adds a new item (or items) to the end of the array
pop pulls the last item off an array and returns it for use
- let colors = ["blue", "red", "green"];
- colors.push("gold"); //["blue", "red", "green", "gold"]
- let lastColor = colors.pop(); //lastColor --> "gold"
- colors.pop(); //this returns "green"
- //colors array is now just: ["blue", "red"]
Shift and Unshift:
Another pair of methods is called .shift() and .unshift(item). These are like pop and push, but they work at the front of the array.
shift removes the first item and shifts everything down, leaving no gaps
unshift pushes everything back and inserts a new item (or items) at index
0
- let numbers = [317, 12, -8402];
- numbers.shift(); //317; numbers is now [12, -8402]
- let nextNumber = numbers.shift(); //nextNumber = 12
- numbers.unshift(42, 98); //[42, 98, -8402]