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Editor to share with you how to use the findIndex function in JavaScript, I believe most people do not know much about it, so share this article for your reference, I hope you can learn a lot after reading this article, let's go to know it!

FindIndex function

Syntax: arr.findIndex (callbackFn [, thisArg])

Method function: returns the value of the first element in the array that satisfies the provided test function. Otherwise, undefined is returned.

Return: the index of the first element in the array by providing the test function. Otherwise, return-1.

Custom function: myFindIndex.

Array.prototype.myFindIndex = function (callbackFn, thisArg) {if (typeof callbackFn! = = 'function') throw (' callbackFn parameter must be a function'); let element = this, len = element & & element.length | | 0; if (! thisArg) thisArg = element; for (let index = 0; index < len; index++) {if (callbackFn.call (thisArg, element [index], index, element) return index;} return-1;} what JavaScript can do. It can make web pages interactive, such as responding to user clicks and providing users with a better experience. two。 You can process forms, verify user input, and provide timely feedback to save users time. 3. The page can be created dynamically according to the user's operation. 4 using JavaScript, you can set up some temporary information that cookie stores on the browser.

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