See the tutorial on JavaScript ES6 Features to learn more about arrow function notation. The some() method is supported in all major browsers, such as Chrome, Firefox, IE (9 and above), etc. Likewise, two distinct arrays are not equal even if they have the same values in the same order. Because, two distinct objects are not equal even if they look the same (i.e. Var persons = [) it will not work (always return -1). If it's not added, we should remedy that: const el = document. But first, let's take a look at the signature - bearing in mind that this is for he DOMTokenList: contains (token )įor our example let's assume that we have a simple h1 element with two CSS classes: My title Īnd that we'd like to check if a particular CSS class is added to the element programatically.
Let's take a look at the second point because I had a very specific task at hand, and it took me some time to figure out what I was doing wrong. There are a number of places where this method can be called/used: Now that we have exhausted the use-cases for includes() let's turn our focus to contains(). (Where the location is inclusive.)Ī few examples can be seen below for both versions. In terms of the signature and return value, the behaviour is the same as discussed before, except of course that the second, optional parameter, is not an array index but a position within the string. Includes() can also be used with strings, where a case-sensitive search is performed if a string is part of a larger corpus of text or not. Please note that if index is greater than or equal to array.length the search will not be performed and false will be automatically returned by includes(). The second parameter defines a position within the array at which the search should begin for the element provided in parameter one. The elementToFind parameter is rather straight forward - this is what specifies what element we are looking for. Includes() for arrays takes two parameters where the second one is optional: includes (elementToFind, index ) We'll focus on the first two use-cases as those seem to be more common than the other two. There are four ways that the includes() method can be used in JavaScript today:
In JavaScript the method we need to use is called includes but that being said, JavaScript also has a contains method but it is for a slightly different purpose. Also, if you come from a different language, for example Java, you'd also be used to using contains on an ArrayList. The optional second argument fromIndex defaults to 0 (i.e. Admittedly when it comes to working with JavaScript and arrays, intiutively a lot of people would choose the contains method to check if the array - well, you guessed right, "contains" - an element. The includes method 1 is defined as: includes compares searchElement to the elements of the array, in ascending order, using the SameValueZero algorithm, and if found at any position, returns true otherwise, false is returned.
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