The technical term for this equality check is sameValueZero. The Array#includes() function will find NaN in an array. Semantics as the = operator (no type coercion), with the exception The Array#includes() function checks for equality using the same It takes a parameter valueToFind, and returns true if some element in the array is equal to valueToFind. The Array#includes() function was introduced in ECMAScript 2016. To determine whether arr contains the string 'B', you can use Array#includes() or Array#indexOf(). Suppose you have a simple array with 3 elements: const arr = It almost looks like a regular English sentence.Given a JavaScript array, there are two built-in array methods you can use to determine whether the array contains a given element. Finally, notice how the includes method helps with readability. The includes method fixes that behavior and correctly returns true, even for NaN. This is because NaN is not considered to be equal to itself, index of does not find it in the array.

Call the index of method and try to find NaN. Now, create an array of numbers that includes the special not a number value or NaN. 16 is one of the last three items, but it's not one of the last two. Specify a negative value to come from the end of the array. If you change the four to a five, the return value will be false. The return value will be true, because 16 is exactly at index four. Go ahead and search the value 16 starting at the index four. It specifies the array position at which to start the search. The includes method accepts an optional second parameter called from index. It determines whether an array includes a certain element and returns true or false as appropriate. A better approach is to use the includes method, which was standardized in ES 2016.

The result will be true for all items in the array and false otherwise. IndexOf will return either the items index, or -1 if the array does not contain the item. The traditional approach is to call the indexOf method with a given item. Let's say you need to find out if this array contains the value 16. To get started, open the node REPL and create an array with a bunch of numbers.

Javascript check if array