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 and inefficient. Instead, I use the following algorithm:
For instance methods, always call with the base object or with
call/apply. Don't use `this` in methods that are to be called as
static, so you can use variable shortcuts for those static methods,
pass them around.
// DONT DO THIS
var StyleUtils = {
HAS_COMPUTED_STYLE : (function() { /*...*/ return true; })(),
getStyle : function(el, name) {
// FAILED STRATEGY, `this` in static context.
if(this.HAS_COMPUTED_STYLE) {
return "worked";
}
return "didn't work";
}
};
That most JavaScript programmers like to bind every function says more
about trends in JavaScript programming than about JavaScript.
> 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.
var o = {
m : function(){ alert( this == o ); }
};
o.m(); // true, o is base object
var f = o.m;
f(); // false.
Calling f() results false because the base object is a declarative
environment record (called VariableObject in ES3). And when that
happens, the `this` value is either global object or null in ES5 in
some cases.
--
Garrett
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