Question

71

JavaScript filter that stops at the first result

rated 0 times [ 75] [ 4] / answers: 1 / hits: 45679 / 7 Years ago, fri, january 20, 2017, 12:00:00

Is there a mechanism in JavaScript (without having to write my own) similar to filter. Instead of returning all the filtered elements of a collection though, it only returns the first one. Of course I could do the following to get the first even number:

[7,5,3,2,1].filter(x => x % 2 == 0)[0]

But if there were 10 million more numbers in that list, there'd be a lot of unnecessary work. In a language like Haskell, the other 10 million numbers wouldn't be looked at due to lazy evaluation.

Is there a mechanism in JavaScript to do the above without evaluating any elements after the first result?

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jamaal

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3 Years ago

answered 7 Years ago mckenna · Accepted Answer

You can try .find:

[7,5,3,2,1].find(x => x % 2 == 0);

// result: 2

From the docs:

The find() method returns a value of the first element in the array
that satisfies the provided testing function. Otherwise undefined is
returned.

Simple benchmark

var arr = [...Array(10000)].map( (item, idx) => idx )



arr.filter(i => i == 3000)[0]

arr.find(i => i == 3000)



/*

  arr.filter x 1,358 ops/sec ±0.40% (91 runs sampled)

  arr.find x 23,743 ops/sec ±0.40% (90 runs sampled)

  Fastest is arr.find

*/