Checking with includes

Learn to check whether an element is in the array with includes.

Checking membership with includes

The includes method returns a boolean telling whether an element is in the array.

Example: ["apple", "pear"].includes("apple") returns true. If it cannot find the element, it returns false.

Unlike indexOf, you do not deal with -1; you can write if (arr.includes(x)) directly. It also takes a start index as a second argument.

includes versus indexOf

includes returns true/false directly; indexOf returns an index.

For the question "is this element in the array?", includes is more readable: if (arr.includes(x)) versus if (arr.indexOf(x) !== -1).

Both walk the array front to back. The performance difference is usually negligible; includes is preferred for readability.

Exercise Check whether a tag exists in the tags array

Create an array named tags with at least three tag strings. Use tags.includes to check whether a tag exists and print the result with console.log.

Show example solution

Write the array, then check a tag with tags.includes and print the result with console.log.
Example solution:
const tags = ["js", "css", "html"];
const hasJs = tags.includes("js");
console.log(hasJs);

Test yourself

Check whether cat is among the pets

const pets = ["cat", "dog", "bird"];
const hasCat = pets.includes(____);
console.log(hasCat);

Show answer

const pets = ["cat", "dog", "bird"];
const hasCat = pets.includes("cat");
console.log(hasCat);

What does this code print?
```
const nums = [10, 20, 30];
console.log(nums.includes(25));
```
- true
- 0
- -1
- false
Show answer

false — Correct. 25 is not in the array; includes returns false.
Match each method with its return value

includes

returns true/false
indexOf

returns an index
includes when not found

returns false

Next lesson: findIndex and some

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