On May 20, 2010, at 11:37 AM, Irakli Gozalishvili wrote:
> Hi,
>
> Sorry if my question is stupid or does not really belongs here. I will be
> thankful to get some clarification on es specs since I just discovered that
> my interpretation of how getter / setters are supposed to behave appears to
> be different from the behavior in observed in modern browsers.
>
> var foo = Object.create({}, {
> bar: {
> get: function() {
> return this._foo;
> },
> set: function(value) {
> return this._foo = 'Hello ' + value;
> }
> }
> });
>
> var bar = foo.bar = 'setter';
> if (foo.bar !== bar) throw new Error('Unexpected');
>
> The code will throw an error cause bar will be 'setter' while foo.bar will be
> 'Hello setter'. I was expecting that `bar' would've get value returned by a
> setter (or at least getter of foo). And this is not the case nor with FF nor
> with Safari implementations. Behavior is the same if getters and setters are
> used instead. Is it expected behavior ? If answer is yes, is there any point
> of returning anything from setter ?
There is no point in returning anything from a setter.
This is due to the semantics of the assignment operator, not setters -- the
result value of an assignment is the righthand side of the expression.
eg. for any expression
<some lvalue> = someObject.property = <expr>
the behaviour is equivalent to
temp = <expr>
someObject.property = temp
<some lvalue> = temp
(ignoring the need to resolve the destinations in the correct order)
> I am also afraid that this might break some of the frameworks in rare cases
> like in this example above. (a = b = c is commonly used syntax)
This has always been the behaviour of assignment.
--Oliver
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