Introducing smap.js, a forward polyfill for ES6 Maps (opens in new tab)

(eriwen.com)

13 pointsdevnulled13y ago9 comments

9 comments

I have quite a few questions about this implementation, but here are two bigger ones:

1. Why are constructed Maps here having delete, get, has, set, size, keys, values, and iterate added outside of the prototype? I guess I don't see why you wouldn't just put these on the prototype. That said, .call seems to be unnecessary in a lot of this code.

2. Why isn't there any attempt to make lookups for primitives faster. It's all O(n).

watmough13y ago

For anyone confused, like me, about what a forward polyfill is, here's an explanation:

http://www.jonathantneal.com/blog/polyfills-and-prototypes/

FuzzyDunlop13y ago

    var NULL = null, TRUE = true, FALSE = false

I'm not sure I understand this. Why assign these to variables?

esrauch13y ago

I think the reason for these is for js minification. With these assignments a simple minifier will replace those three variables with a line like this:

    var a=null,b=true,c=false;

Then your minified js will be smaller because all other instances of true, false and null will be one character. Whether or not this is a reasonable optimization is debatable but in terms of pure code size it would be a win.

ajanuary13y ago

Couldn't you build it into the minifier rather than polluting the original source?

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wendelinsky13y ago

That is part of the es6-collections polyfill included as part of smap.js. If I understand correctly, it is for safety (for example you cannot override the value of "true").

Twisol13y ago

null, true, and false are all keywords. Isn't undefined the only one that can be redefined? (And then it's just equal to void 0.)

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9 comments

just2n13y ago

I have quite a few questions about this implementation, but here are two bigger ones:

2. Why isn't there any attempt to make lookups for primitives faster. It's all O(n).

watmough13y ago

For anyone confused, like me, about what a forward polyfill is, here's an explanation:

http://www.jonathantneal.com/blog/polyfills-and-prototypes/

FuzzyDunlop13y ago

    var NULL = null, TRUE = true, FALSE = false

I'm not sure I understand this. Why assign these to variables?

esrauch13y ago

I think the reason for these is for js minification. With these assignments a simple minifier will replace those three variables with a line like this:

    var a=null,b=true,c=false;

ajanuary13y ago

Couldn't you build it into the minifier rather than polluting the original source?

1 more reply

wendelinsky13y ago

That is part of the es6-collections polyfill included as part of smap.js. If I understand correctly, it is for safety (for example you cannot override the value of "true").

Twisol13y ago

null, true, and false are all keywords. Isn't undefined the only one that can be redefined? (And then it's just equal to void 0.)

1 more reply

j / k navigate · click thread line to collapse