Nov 24, 2009 · Usually I would expect a String.contains() method, but there doesn't seem to be one. What is a reasonable way to check for this?

16 ES6 contains inbuilt method (includes) in String's prototype, which can be used to check if string contains another string or not.

What is the most concise and efficient way to find out if a JavaScript array contains a value? This is the only way I know to do it: function contains(a, obj) { for (var i = 0; i < a.length;...

Jul 8, 2009 · How do I check if a particular key exists in a JavaScript object or array? If a key doesn't exist, and I try to access it, will it return false? Or throw an error?

Oct 22, 2012 · Possible Duplicate: JavaScript: string contains I have a postcode variable and want to use JS to add a location into a different variable when the postcode is changed/entered. So …

2023 This question already has answers here: How do I check if an object has a specific property in JavaScript? (33 answers)

Jul 23, 2017 · 261 I'm working with a performance issue on JavaScript. So I just want to ask: what is the fastest way to check whether a string contains another substring (I just need the boolean …

Using plain JavaScript (not jQuery), Is there any way to check if an element contains a class? Currently, I'm doing this: var test = document.getElementById("test"); var testClass = test.cla...

1168 This question already has answers here: How to check whether a string contains a substring in JavaScript? (3 answers)

Oct 2, 2012 · In the first alert (), JavaScript returned "-1" - in other words, indexOf () did not find a match: this is simply because "JavaScript" is in lowercase in the first string, and properly …