Does JavaScript have an indexOf(lambda) or similar?

Question

I want to return the index of the first element satisfying a unary predicate.

Example:

[1,2,3,4,5,6,7].indexOf((x) => x % 3 === 0) // returns 2

Is there such a function? The alternative I was going to use was

[1,2,3,4,5,6,7].reduce((retval,curelem,idx) => 
{
   if(curelem % 3 === 0 && retval === undefined)
       retval = idx; 
   return retval;
}, undefined);

but of course that would be less efficient since it doesn't stop iterating through the array after it has found the element.

@Vohuman post it as an answer (with an example and couple more words) and I'll upvote you — zerkms
– zerkms, Commented Jul 10, 2016 at 21:46

Ram · Accepted Answer · 2016-07-10 21:51:48Z

35

Yes, there is such function: Array.prototype.findIndex. The method was introduced by ECMAScript 2015 and you need to use a polyfill for supporting older browsers.

edited Jul 10, 2016 at 21:51

answered Jul 10, 2016 at 21:49

Ram

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2 Comments

zerkms Over a year ago

"and it works just like the lambd function" --- this statement looks weird.

zerkms Over a year ago

Well, I cannot think of what it means actually. I don't know that it means for something "to work like the lambda function". To me (since the standard does not provide an official definition for that), a lambda function === a function expression.

kevin ternet · Accepted Answer · 2016-07-10 21:49:38Z

15

yes it exists :

console.log([1,2,3,4,5,6,7].findIndex((x) => x % 3 === 0));

answered Jul 10, 2016 at 21:49

kevin ternet

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