Arrays

Arrays hold lists

• An array is an ordered list of values in [ ... ].
• Reach an item by its index, counting from 0: arr[0] is the first.
• .length tells you how many items there are.

let nums = [10, 20, 30];
console.log(nums[0]);        // → 10
console.log(nums.length);    // → 3

Add and remove items

• .push(x) adds x to the end; .pop() removes the last item.
• The array grows and shrinks as you go.

let nums = [10, 20, 30];
nums.push(40);
console.log(nums);   // → [10,20,30,40]
nums.pop();
console.log(nums);   // → [10,20,30]

Loop over an array

• A for loop with an index visits each item, from 0 to length - 1.

let nums = [1, 2, 3];
for (let i = 0; i < nums.length; i++) {
  console.log(nums[i]);   // → 1, then 2, then 3
}

Common mistakes

• Index from 0; a.length is the size.
• push adds to the end; pop removes from the end.

Now you try

• Use an index, or a loop, on each array.
• Press Check answer to test it.