Add replacement for String.startsWith

[jfmengels]

I noticed that String.startsWith can be very slow for large strings when the str does not contain the prefix. The reason being the function actually does a str.indexOf call which will go through the entire function as long as it doesn't find anything.

So I tried benchmarking alternatives.

I tried using the ES2015 startsWith, which is by far faster but doesn't work on IE.

And I also tried another version where we slice the string and compare that to the prefix.

Benchmark

Chrome

Firefox

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What do you think of the idea of replacing String.startsWith? Does that sound good?

Maybe we can do something faster in JS where we compare every character one by one.

I also think similar improvements can be made for String.endsWith.

[jfmengels]

Maybe we can do something faster in JS where we compare every character one by one.

I just tested that and that is by far the fastest (even faster than the native startsWith in FF). The screenshots above now reflect that.