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// Here is a proposal for minimalist JavaScript classes, humbly offered.
// There are (at least) two different directions in which classes can be steered.
// If we go for a wholly new semantics and implementation, then fancier classical
// inheritance can be supported with parallel prototype chains for true inheritance
// of properties at both the class and instance level.
// If however, we keep current JavaScript prototype semantics, and add a form that
// can desugar to ES3, things must necessarily stay simpler. This is the direction
// I'm assuming here.
// If we want to have static class bodies (no executable code at the top level),
// then we would do well to reuse the known and loved JavaScript idiom for
// fixed lists of properties -- the object literal.
// First, basic usage from a real-world library (Three.js)
class Color {
constructor: function(hex) {
...
},
r: 1, g: 1, b: 1,
copy: function(color) {
...
},
setRGB: function(r, g, b) {
...
},
setHSV: function(h, s, v) {
...
}
}
// To create a class with its prototype chain set correctly:
class Fox extends Animal {
...
}
// Note that "Animal" here is a class object (constructor function) in its
// own right. Fox.prototype is set to an instance of Animal that has been
// constructed without calling its constructor function -- this is the
// usual two-step setting-up-a-prototype shuffle.
// There is no special syntax for setting class-level properties, as they are
// relatively rare. Just add them to the class object itself:
Fox.CONSTANT = value;
// Note that the right-hand side of a class definition is just an expression,
// an object literal is not required. You can be fully dynamic when creating a
// class:
class Student objectContainingStudentProperties
// Or even:
class Protester merge(YoungAdult, WorkEthic, Idealism, {
student: true
})
// The point I'm trying to make being that the own properties of the right hand
// side, however they're derived, become the prototypal properties of the resulting
// class.
// Similarly, class definitions are themselves expressions, and anonymous classes
// are equally possible:
animals.push(class Fox {});
var subclass = function(parent) {
return class extends parent;
};
// Naturally, classes can be built up programmatically in this fashion.
var generateModelClass = function(columns) {
var definition = {};
columns.forEach(function(col) {
definition['get' + col] = function() {
return this[col];
};
definition['set' + col] = function(value) {
return this[col] = value;
};
});
return class definition;
};
// Finally, the Monster class from the current nutshell proposal
// (http://wiki.ecmascript.org/doku.php?id=harmony:classes#the_proposal_in_a_nutshell)
// ... sans unnecessary restrictions:
class Monster {
constructor: function(name, health) {
this.name = name;
this.health = health;
},
attack: function(target) {
log("The monster attacks " + target);
},
isAlive: function() {
return this.health > 0;
},
setHealth: function(value) {
if (value < 0) {
throw new Error("Health must be non-negative.");
}
this.health = value;
},
numAttacks: 0,
attackMessage: "The monster hits you!"
}
// I think that's about the run of it. Note what is left out: public / private /
// static / frozen / const properties and their ilk. Personally, I'm of the view
// that all of these modifiers are deeply undesirable in a language as dynamic
// as JavaScript and won't be much used, if added ... but I also think that
// getters and setters should be deprecated and removed.
// If public / private / static / frozen / const must be a part of class syntax
// in JS.next, then they must be valid prefixes for object literals as well --
// and can easily be used to define classes with those properties under this
// proposal.
// There are no new semantics here, and these classes can easily be transpiled
// into ES3 if needed -- just simpler declaration of constructors with prototypal
// properties and correctly configured prototype chains.
// tl;dr
// Classes are a new expression with the form ([] means optional):
// class [name] [extends parent] [expression]
@naholyr
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naholyr commented Nov 2, 2011

Why not just using popular coffeescript implementation ?

@nzakas
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nzakas commented Nov 2, 2011

Very interesting stuff. I wonder if there's a way to split the difference. It looks like ES6 has the concept of StructType, which is a constructor that accepts an object literal defining how it should behave. So why not do the same for classes (or as I prefer to call them, types):

var Color = new Type({

  constructor: function(hex) {
    ...
  },

  r: 1, g: 1, b: 1,

  copy: function(color) {
    ...
  },

  setRGB: function(r, g, b) {
    ...
  },

  setHSV: function(h, s, v) {
    ...
  }

});

This fits into the paradigms being introduced in ES6, allows you to define a type easily with an object literal, and doesn't introduce new syntax. It would at least be a baby step towards the end goal of more easily defining custom types.

@tj
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tj commented Nov 2, 2011

it's kinda sad that ES people can't come up with something minimal like this. It looks much nicer than the horrid proposal, so for that I would +1 it I guess, though I think classes are pretty restrictive, not the inheritance model I would want.

"but I also think that
// getters and setters should be deprecated and removed." - I agree 100%, proxies too

@anentropic
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anentropic commented Nov 2, 2011

Looks nice!!

"Note what is left out: public / private / static / frozen / const properties and their ilk. Personally, I'm of the view that all of these modifiers are deeply undesirable in a language as dynamic as JavaScript and won't be much used, if added"

I'm of the more pessimistic view that they should be left out because they will be used everywhere if added :)

@rwaldron
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rwaldron commented Nov 2, 2011

@visionmedia I'm curious, why the opposition to Proxy?

@tj
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tj commented Nov 2, 2011

@rwldrn probably not the right thread for that. new gist? haha :D

@rwaldron
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rwaldron commented Nov 2, 2011

@visionmedia - Sure, but you brought it up here 0_o

@tj
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tj commented Nov 2, 2011

@rwldrn https://gist.github.com/1334751
no point spamming this gist

@juandopazo
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juandopazo commented Nov 3, 2011

I'm really glad to see the community react so positively to classes as annotated object literals. I hope T39 listens to it :D

@Garciat
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Garciat commented Nov 3, 2011

I like it. It is very JavaScript-like, and that is what we should be aiming for. The new class syntax should be nothing but shortcuts for what we today do manually. Anything else beyond that is just drifting away from true JS.

@BrendanEich
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BrendanEich commented Nov 3, 2011

@juandopazo: you read es-discuss, so you should know that @allenwb and others have been pursuing class bodies as object literals. That didn't start here. Thanks to @jashkenas for rekindling it and using a gist (gist + email >> email), but your TC39 vs. the community spin is kinda lousy. Credit where due.

/be

@juandopazo
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juandopazo commented Nov 3, 2011

@BrendanEich absolutely! In fact my first comment on this gist has a link to @allenwb 's first proposal. I meant no disrespect at all.

@jiggliemon
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jiggliemon commented Nov 4, 2011

I like how the ES proposal drops the function statement on class methods.

@tj
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tj commented Nov 4, 2011

@jiggliemon it's inconsistent, more grammar is not necessarily a better thing, it's easier for people catch on if you utilize what's already there. I dont personally se "function" as a problem, but that's the thing worth tackling in a consistent manner

@chrisdickinson
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chrisdickinson commented Jan 7, 2012

Hey, I've got a hacked-up implementation of this proposal here. It also adds two new operators (strong binding unary and binary :), as well as multiline strings.

I'd love some thoughts!

@geddski
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geddski commented Mar 23, 2012

I'll always remember this as the sad day when spammers found out about github. Report @StevenGerrard.

@wjcrowcroft
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wjcrowcroft commented Mar 23, 2012

@csuwildcat
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csuwildcat commented Mar 23, 2012

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