CODEWITHSUNDEEP
javascriptarrays
jlynch630
jlynch630

Reputation: 697

Why is deleting from an object faster than splicing array?

I was curious to see the speed differences between arrays and objects, so I set up a test for filling, accessing, and deleting 100,000 items from an array and object. Accessing and filling the array were about equal with a ~3ms difference. Deleting from the array, however, resulted in 604ms difference(10ms vs 614ms). Why is this? I thought objects and arrays were pretty much the same.

Demo: https://codecanister.com/Project/b9f8de7c/1/result/

Upvotes: 1

Views: 816

Answers (2)

Mick
Mick

Reputation: 8922

You just perform different actions. "delete" will just set the array-position to undefined. While splice will totally remove it by performing a loop with arr[i] = arr[i+1] for all 10,000 items of your array. You do this for all 10.000 items. See also this question

Upvotes: 0

Pointy
Pointy

Reputation: 413966

When you do that .splice(), all the subsequent array entries have to be reassigned. That is, every property name after the one spliced out must be changed. There's no good way to do that except a straight linear traversal of the properties; a data structure that made that operation fast would make other, more common operations slower.

So consider the array [1, 2, 3, 4]. The value of property "0" is 1. If you splice that entry out, then the runtime has to set property "0" to 2, property "1" to 3, and property "2" to 4.

Upvotes: 3

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