Javascript optional type hinting

javascript performance variables ecmascript-harmony ecmascript-4
badunk picture badunk · Sep 12, 2012 · Viewed 19.7k times · Source

When a programming language is statically typed, the compiler can be more precise about memory allocation and thus be generally more performant (with all other things equal).

I believe ES4 introduced optional type hinting (from what I understand, Adobe had a huge part in contributing to its spec due to actionscript). Does javascript officially support type hinting as a result? Will ES6 support optional type hinting for native variables?

If Javascript does support type hinting, are there any benchmarks that show how it pays off in terms of performance? I have not seen an open source project use this yet.

Answer

Jeremy J Starcher picture Jeremy J Starcher · Sep 12, 2012

My understanding, from listening to many Javascript talks on the various sites, is that type-hinting won't do as much to help as people think it will.

In short, most Javascript objects tend to have the same "shape", if you will. That is, they will have the same properties created in the same order. This "shape" can be thought of as the "type" of the object. An example:

function Point(x, y) {
  this.x = x;
  this.y = y;
}

All objects made from "Point" will have the same "shape" and the newer internal Javascript engines can do some fancy games to get faster lookup.

In Chrome (perhaps others), they use a high-bit flag to indicate if the rest of the number is an integer or a pointer.

With all of these fancy things going on, that just leaves typing for the human coders. I, for one, really like not having to worry about type and wouldn't use that feature.

You are semi-correct, though. Type hinting is a part of ActionScript 3 which is a derivative of ECMAScript -- but hinting has never made it into the standard. AFAIK, outside of wishful thinking, it hasn't been discussed.

This video describes things in far more detail: http://www.youtube.com/watch?v=FrufJFBSoQY

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