console.log(firstTrough); // 1
    

###  Using findIndex() on sparse arrays

You can search for ` undefined ` in a sparse array and get the index of an
empty slot.

js

    
    
    console.log([1, , 3].findIndex((x) => x === undefined)); // 1
    

###  Calling findIndex() on non-array objects

The ` findIndex() ` method reads the ` length ` property of ` this ` and then
accesses each property whose key is a nonnegative integer less than ` length `
.

js

    
    
    const arrayLike = {
      length: 3,
      "-1": 0.1, // ignored by findIndex() since -1 < 0
      0: 2,
      1: 7.3,
      2: 4,
    };
    console.log(
      Array.prototype.findIndex.call(arrayLike, (x) => !Number.isInteger(x)),
    ); // 1
    

##  Specifications

Specification  
---  
[ ECMAScript Language Specification  
#  sec-array.prototype.findindex  ](https://tc39.es/ecma262/multipage/indexed-
collections.html#sec-array.prototype.findindex)  
  
##  Browser compatibility

BCD tables only load in the browser  with JavaScript enabled. Enable
JavaScript to view data.

##  See also

  * [ Polyfill of ` Array.prototype.findIndex ` in ` core-js ` ](https://github.com/zloirock/core-js#ecmascript-array)
  * [ Indexed collections ](/en-US/docs/Web/JavaScript/Guide/Indexed_collections) guide 
  * [ ` Array ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array)
  * [ ` Array.prototype.find() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find)
  * [ ` Array.prototype.findLast() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/findLast)
  * [ ` Array.prototype.findLastIndex() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/findLastIndex)
  * [ ` Array.prototype.indexOf() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/indexOf)
  * [ ` Array.prototype.lastIndexOf() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/lastIndexOf)
  * [ ` TypedArray.prototype.findIndex() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/findIndex)

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