On 4/11/11, Claus Reinke <[email protected]> wrote:
> Like most Javascript programmers, I have tended to follow
> a simple rule for functions using 'this': eta-expand method
> selections, use .bind, or get into trouble.
>
That is unnecessary, inefficient, and adds clutter.
That most JavaScript programmers do that says more about trends in
JavaScript programming than it does about the language.
> Then I got curious about how method calls determine what
> object to pass as 'this': a method is a function selected from
> an object, and functions are first-class values, so, by the time
> they get called, how do we know where they came from?
>
The base object.
Follow these two rules to greatly reduce `this` reference confusion.
1. For instance methods (such as prototype methods), either qualify
the method call with the base object or use call/apply. For example,
var x = new X;
x.m(); // Qualified instance method
// DONT DO THIS
var m = x.m;
m();
2. For static methods, write them so that they never use `this`. For
example, here is an example of static method `getStyle` that violates
that rule and uses `this`:
// DONT DO THIS
var StyleUtils = {
HAS_COMPUTED_STYLE : (function() { /*...*/})(),
getStyle : function(el, name) {
// Problem: Use of `this` in static method.
if(this.HAS_COMPUTED_STYLE) {
}
}
};
By never using `this` in static methods, it can be assured that they
can be aliased with a variable and passed around, e.g. `var getStyle =
StyleUtils.getStyle`.
--
Garrett
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