Checking if an array includes a value is something that we’ve to do often in a JavaScript app.
In this article, we’ll look at how to check if an array includes a given value in JavaScript.
Array.prototype.includes
The includes method is a method that’s included with the array instance.
It takes a value and compares it with === to check if an element is included.
For instance, we can write:
console.log(['apple', 'orange', 'grape'].includes('orange'));
If it’s included, then it returns true .
Otherwise, it returns false .
Array.prototype.indexOf
We can also use the indexOf method of an array instance to check if it includes a given element.
It also uses === for comparison.
And it returns the index of the first instance of an item if it exists.
Otherwise, it returns -1.
To use it, we write:
console.log(['apple', 'orange', 'grape'].indexOf('orange') >= 0);
Write Our Own
We can write our own function to search for a value.
For instance, we can write:
function contains(a, obj) {
let i = a.length;
while (i--) {
if (a[i] === obj) {
return true;
}
}
return false;
}
console.log(contains(['apple', 'orange', 'grape'] , 'orange'));
We create the contains function that uses a while loop to search for an item.
If a[i] has the same value as obj then we return true .
If we loop through the whole a array and didn’t find anything that matches, then we return false .
Array.prototype.some
The some method is another array instance method that comes with JavaScript arrays.
It lets us pass in a callback to check if any items match the given condition.
For instance, we can write:
const items = [{
a: '1'
}, {
a: '2'
}, {
a: '3'
}]
console.log(items.some(item => item.a === '3'))
We have an items array that has a bunch of objects.
And we call items.some with a callback to check if any items entry with a property equal to 3 exists.
some returns true if an item that matches the given condition exists and false otherwise.
Conclusion
There’re many ways to find if an array item exists in JavaScript.
