Arrays

An array is an ordered list of values. You met arrays in the variables lesson. Now let’s do things with them.

const fruits = ["apple", "banana", "pineapple"];
//  index:         0         1          2

Adding and removing

<script>
const queue = ["Emma", "Diego"];

queue.push("Sofia");
console.log("After push:", queue);

const served = queue.shift();
console.log("Served:", served);
console.log("Still waiting:", queue);
console.log("How many:", queue.length);
</script>

Searching

• includes(x) gives true or false.
• indexOf(x) gives the position, or -1 if it isn’t there.
• find(fn) gives the first item that passes a test.

Transforming: map, filter and forEach

These three take a function and run it on every item. They replace most loops.

<script>
const prices = [40, 250, 90, 120, 60];

const halfOff = prices.map((p) => p / 2);
console.log("Half off:", halfOff);

const cheap = prices.filter((p) => p < 100);
console.log("Under 100:", cheap);

const total = prices.reduce((sum, p) => sum + p, 0);
console.log("Total:", total);

prices.forEach((p, i) => console.log("Item " + i + " costs " + p));
</script>

map and filter never change the original array. They hand you a new one.

Joining into text

join() turns an array into one string:

["HTML", "CSS", "JavaScript"].join(", "); // "HTML, CSS, JavaScript"