Let's try searching for a number that doesn't exist in the array. We got true returned because 3 exists in the nums array. In the includes() method's parameter, we passed in 3. Using dot notation, we attached the includes() method to the nums array. In the example above, we created an array called nums with four numbers – 1, 3, 5, 7. Here are some examples to show how to use the includes() method to check if an item exists in an array: const nums = If you don't include this parameter, the default index will be set to 0 (the first index). fromIndex, which is an optional parameter, specifies the index from which to start the search.item is the particular item you are searching for.The includes() method takes in two parameters – item and fromIndex. Here's the syntax for using the includes() method to check if an item is in an array: array.includes(item, fromIndex)Īrray denotes the name of the array which will be searched through to check if an item exists. How to Check if an Item is in an Array in JavaScript Using Array.includes() In this article, you'll see how to use the includes() method in JavaScript to check if an item is in an Array, and if a substring exists within a string. It returns true if the item is found in the array/string and false if the item doesn't exist. You can also use it to check if a substring exists within a string. So you may want to rewrite your code as follows: function contains(a, obj) )) //falseĬonsole.log(.You can use the includes() method in JavaScript to check if an item exists in an array. If you need the best performance, benchmark for yourself in the relevant execution environments.Īs others have said, the iteration through the array is probably the best way, but it has been proven that a decreasing while loop is the fastest way to iterate in JavaScript. If you need an easy solution, look for other answers. It might not be relevant to modern JS execution contexts. The promised performance improvement was based on a benchmark done in browsers of that time. Update from 2019: This answer is from 2008 (11 years old!) and is not relevant for modern JS usage.
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