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The big bug as I see it is: obj = { get_name = function() { return "I am an object" }, func = function() { alert(this.get_name()); } } This lo

The big bug as I see it is: obj = { get_name = function() { return "I am an object" }, func = function() { alert(this.get_name()); } } This looks dandy, and obj.func() works as expected. but if you pass obj.func as a callback, the this when its invoked will be some other object (by default, the window object): button.onclick = obj.func; // bang when invoked The number of times I got screwed by that. You end up having to have little anonymous functions for all callbacks: button.onclick = function(evt) { obj.func(); } (apologies for bugs; just typing javascript from memory) (would love to be wrong)

locci 14y ago
bind was introduced in ES5 (and previously in most libraries) to fix this https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Function/bind https://developer.mozilla.org/en-US/docs/JavaScript/Referenc...
- huskyr 14y ago
  And trivially easy to shim for older browsers. I would really recommend using Function.prototype.bind instead of the 'var self = this' or library bind functions (such as $.proxy), it's just the way it should be written :)
  - jessaustin 14y ago
    To confirm my understanding, would the erroneous line from the comment above be rewritten like: button.onclick = obj.func.bind(obj); So un-DRY! It's almost admirable, how blatant a hack this is.
politician 14y ago
It clicked for me when I decided that there were no methods and considered all function invocations to be special cases of `apply`. Then the case you mentioned becomes a bog standard case of a property lookup, and the callback becomes a case of `apply(window, [args])`. tldr: JavaScript has functions, not methods :)
bazsouthafrica 14y ago
This is exactly the catch with respect to function invocation method that I was trying to point out. It seems that in a call back method, `this` gets bound to the global object. I suspect it is because it is called with the same mechanism that is used for function invocation. That being said, I did not use this example because one needs to implement a callback to see the error. My example that I chose in my article was designed so that anyone could just create the JavaScript, fire it up in a browser, and see the error for themselves. I do however intend to use an example similar to the one you have presented when I cover closures and scoping in JavaScript.

locci 14y ago

bind was introduced in ES5 (and previously in most libraries) to fix this https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Function/bind https://developer.mozilla.org/en-US/docs/JavaScript/Referenc...

huskyr 14y ago
And trivially easy to shim for older browsers. I would really recommend using Function.prototype.bind instead of the 'var self = this' or library bind functions (such as $.proxy), it's just the way it should be written :)
- jessaustin 14y ago
  To confirm my understanding, would the erroneous line from the comment above be rewritten like: button.onclick = obj.func.bind(obj); So un-DRY! It's almost admirable, how blatant a hack this is.

politician 14y ago

It clicked for me when I decided that there were no methods and considered all function invocations to be special cases of `apply`. Then the case you mentioned becomes a bog standard case of a property lookup, and the callback becomes a case of `apply(window, [args])`. tldr: JavaScript has functions, not methods :)

bazsouthafrica 14y ago

This is exactly the catch with respect to function invocation method that I was trying to point out. It seems that in a call back method, `this` gets bound to the global object. I suspect it is because it is called with the same mechanism that is used for function invocation. That being said, I did not use this example because one needs to implement a callback to see the error. My example that I chose in my article was designed so that anyone could just create the JavaScript, fire it up in a browser, and see the error for themselves. I do however intend to use an example similar to the one you have presented when I cover closures and scoping in JavaScript.