A piece of ordinary boilerplate JavaScript code (original.js) rewritten using proposed moustache syntax (moustache.fixed.js) and class syntax as implemented in Traceur (moustache.class.js)

moustache.class.js

class Channel {
  constructor (opts) {
    /* ... */
  }

  load () {
    var widget = document.createElement("iframe");

    widget.{
      style.{
        width = "100%";
        border = "none";
        overflow = "hidden";
        display = "none";
      };

      dataset.{
        disqusUid = this.uid;
      };

      allowTransparency = true; // < IE8 iframe transparency
      frameBorder = 0;
      width = "100%";
      id = "dsq" + this.uid;
      src = this.target + "#" + this.uid;
    };
  }
};

moustache.fixed.js

var Channel = function (opts) { /* ... */ };

Channel.prototype.load = function () {
  var widget = document.createElement("iframe");

  widget.{
    style.{
      width    = "100%";
      border   = "none";
      overflow = "hidden";
      display  = "none";
    };

    dataset.{
      disqusUid = this.uid;
    };

    allowTransparency = true; // < IE8 iframe transparency
    frameBorder = 0;
    width = "100%";
    id = "dsq" + this.uid;
    src = this.target + "#" + this.uid;
  };
};

moustache.js

var Channel = function (opts) { /* ... */ };

Channel.prototype.load = function () {
  var widget = document.createElement("iframe");

  widget.{
    style.{
      width    = "100%";
      border   = "none";
      overflow = "hidden";
      display  = "none";
    };

    allowTransparency = true; // < IE8 iframe transparency
    frameBorder = 0;
    width = "100%";
    id = "dsq" + this.uid;
    data-disqus-uid = this.uid
    src = this.target + "#" + this.uid;
  };
};

original.js

var Channel = function (opts) { /* ... */ };

Channel.prototype.load = function () {
  var widget = document.createElement('iframe');

  widget.setAttribute('style', 'width:100%; border:none; overflow:hidden; display:none');
  widget.setAttribute('allowTransparency', 'true'); // < IE8 iframe transparency
  widget.setAttribute('frameBorder', '0');
  widget.setAttribute('width', '100%');
  widget.setAttribute('id', 'dsq' + this.uid);
  widget.setAttribute('data-disqus-uid', this.uid);
  widget.setAttribute('src', this.target + '#' + this.uid);

  // ...
};

just want to float this, what is wrong with obj.update({ foo: bar }) or Object.update(obj, {foo: bar})?

this achieves the desired flexibility in nesting without new syntax and is definitely explicitly "updating" the object.

Are there not enough bikesheds?

@ljharb:

So what happens if you do foo.{ bar = true; } when bar isn't a previously defined property on foo?

Same as foo.bar = true; today.

@mikeal:

just want to float this, what is wrong with obj.update({ foo: bar }) or Object.update(obj, {foo: bar})?

I feel like it's similar to your argument against o.{ a = b }. To figure out whether you are defining a new property or updating the current one you will have to check the code to see if it's o.update({ ... }); or o.otherMethod({ ... }); or o = { ... };.

@mikeal: I mostly agree; I don't think "mustache" has been all that well motivated so far. I've been opposed to it for the most part since the beginning, but for me where I started to see some more win was when -- with the variation using assignment syntax -- I realized it could also be used for chaining (aka the fluent style aka cascades) for API's that don't return this for you. For example:

a.{ pop(); pop() }

or

a{ .pop(); .pop() }

or what have you. But I generally agree with you that syntax has to be well-understood and well-motivated to be worth adding. Mustache is definitely not at that point.

Dave

@antonkovalyov

those rules are only as unclear with .update as they are with new syntax. you still have to learn the rules, the only difference is that there is an english word pointing you in the right direction.

@dherman

i agree, it's not compelling enough to me yet to justify the loss in assumptions. while i agree that using : is not clear about updating it doesn't fall in to the trap of stepping on the existing assignment semantics because you already have to look to the top of an object literal definition to understand it.

@mikeal, yeah I agree—was just pointing out that it doesn't solve the unclear rules problem.

sure, not entirely, but it doesn't step on the rules people now assume about assignment statements that exist entirely outside of using this feature.

Object.update, w00t.

We killed <| the other week. I think .{ is going down. But we should really do something like Object.update (Prototype's Object.extend). We talk about paving cowpaths, that's an obvious one and it leads somewhere good.

/be

@BrendanEich, yes, Object.extend (update) was one of the most popular items on JSFixed.

@isaacs Here's a lovely unpainted bikeshed for you: how about Object.update for deep and Object.set for shallow?

Dave

Given the proliferation of subtly different Object.extend implementations, I think this would be a good thing for the ES spec to lay down a decision on. In node, we eventually just removed util.extend entirely, because it was too complicated to satisfy everyone's desires for it to be all things, handling getters and deeply nested objects and so on. New syntax for this is silly, though.

@dherman If I understand you properly, then, Object.update would deep-copy, and Object.set would shallow-copy?

So:

var a = { b: { c: 'd', e: Object.create(Object.prototype, {f: { get: function () { throw 'no can get!' }, configurable: false }}) } }
var b = Object.update({x: 'y'}, a)
var c = Object.set({x: 'y'}, a)

In this example, then, c.b === a.b, b.b !== a.b, and b.b.e is an evil getter?

I have no strong opinions about the method names. set and update are fine. But it is a bad idea to introduce new syntax for this, even though it is cute.

@izs: agree on syntax being bad (premature, unjustified, impossible to polyfill, etc.).

@dherman: first, I wonder if we shouldn't just try to standardize Object.extend as the shallow thing, and make it match prototype but handle enumerable accessors too.

Second thought: naming. The set vs. update names do not connote shallow vs. deep. No name that I know of does, so the boring but clear way is Object.deepExtend. Too long? It's not the common case going by existing libraries I know of.

/be