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November 1, 2011 01:49
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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] |
@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
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!
I'll always remember this as the sad day when spammers found out about github. Report @StevenGerrard.
Hahaha!
Pretty sure they're not going to get the same spam ROI from this
demographic though, morons.
…On Mar 22, 2012 9:21 PM, "Joss Crowcroft" < ***@***.***> wrote:
Hahaha!
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I like how the ES proposal drops the
function
statement on class methods.