Find single or array of values in JavaScript array using includes

I’ve looked at how to find the closest number in a JavaScript array, but what happens when you simply want to check whether a value (or an array of values) exist within that array? Would you like to be able to pass an array to Includes()?

This post will explore how you can find out whether a JavaScript array contains certain values using simple functions to evaluate to true or false. If you want to skip straight to the end there are some ready to go ‘inArray’ style JavaScript functions for you to use.

Look for a single value in an array using includes()

Includes() is a simple array function which returns true if the passed value matches a value within the array.

let haystack = ["12345", "hello", "world"];
let needle = "world";

let result = haystack.includes(needle);

console.log(result); // Output = true

The problem with includes() is that it requires a string value and therefore you can’t pass an array to it. To ‘pass an array’ to includes() we have to try a different approach.

Find an array of values using includes()

So includes() solves the problem of finding out whether a string exists within an array, but what happens if you want to match multiple string values? We could loop, map or filter the values to discover whether they exist, but the array prototype actually has a couple of very useful functions we can utilise.

Checking for a partial match using some()

The first of these is some(). This callback function will loop through an array until one of the conditions evaluates to true:

let haystack = ["12345", "hello", "world"];
let needle = ["world", "banana"];

let result = needle.some(i => haystack.includes(i));

console.log(result); // Output = true

Matching all values using every()

To query the array to match all of the values it is very similar. In this instance we replace some() with every() which evaluates true if all of the conditions are met.

let haystack = ["12345", "hello", "world"];
let needle = ["hello", "12345"];

let result = needle.every(i => haystack.includes(i));

console.log(result); // Output = true

Creating a reusable inArray function

Finally, we can put these approaches together into a reusable function:

function inArray(needle, haystack, matchAll = false) {
    if (matchAll) {
        return needle.every(i => haystack.includes(i));
    } else {
        return needle.some(i => haystack.includes(i));
    }
}

let result = inArray(needle, haystack, true);

Or if you like you could extend the array prototype. By doing this the function becomes available to all arrays. In this instance we are going to use the identifier ‘gb_’ to avoid possible code collisions from other libraries:

Array.prototype.gb_inArray = function(needle, matchAll = false) {
    if (matchAll) {
        return needle.every(i => this.includes(i));
    } else {
        return needle.some(i => this.includes(i));
    }
};

let result = haystack.gb_inArray(needle, true);