Using timers within OO Javascript

[Evan Charlton]

Hey all, I'm having some trouble with window.setInter val() within a
custom object/prototype. Here is my code:

function MyClass() {
// do some junk
// ...
// define methods
this.m_one = function() {
// nothing happens with this line. No alert, no errors
window.setInterval( "this.m_two", 500 );
// "error: this.m_two() is not a function"
window.setInterval( "this.m_two()", 500 );
// "error: m_two() is not defined"
window.setInterval( "m_two()", 500 );
// "error: m_two is not defined"
window.setInterval( "m_two", 500 );
// the following one works just fine .
window.setInterval( "timer()", 500 );
}
this.m_two = function() {
alert("m_two");
}
}
function timer() {
alert("timer");
}
var o = new MyClass();
if( confirm( "start?" ) ){
o.m_one();
}
 

I'm stumped on this one; how do I set another method in the object as
the callback?

[Thomas 'PointedEars' Lahn]

Evan Charlton wrote:

Hey all, I'm having some trouble with window.setInter val() within a
custom object/prototype. Here is my code:

[code]
function MyClass() {

Why are people so obsessed with classes when it comes to OOP? From the
above I thought you had understood that ECMAScript 3 implementations use
only prototype-based inheritance.

// do some junk
// ...
// define methods
this.m_one = function() {
// nothing happens with this line. No alert, no errors
window.setInter val( "this.m_two ", 500 );

Why should there? It is merely a not evaluated read access to the
non-existing property `m_two' *of the Global Object*.

// "error: this.m_two() is not a function"
window.setInter val( "this.m_two ()", 500 );

This is trying to call a method of the Global Object. Since the
identifier cannot be resolved, you get the runtime error.

// "error: m_two() is not defined"
window.setInter val( "m_two()", 500 );

This is trying to call an identifier without an explicit object
reference. Since the identifier cannot be resolved through the scope
chain, you get the runtime error.

// "error: m_two is not defined"
window.setInter val( "m_two", 500 );

This is trying to access an identifier without an explicit object
reference. Since the identifier cannot be resolved through the scope
chain, you get the runtime error.

As you can see, you cannot use a locally defined name in a string for
the window.setInter val() method (it would be the same with
window.setTimeo ut()). However, you can pass a Function object
reference, that is a reference to your method:

window.setInter val(this.m_two, 500);

// the following one works just fine .
window.setInter val( "timer()", 500 );

Because timer() is a globally declared function, and (so) a method of
the Global Object. "this.timer ()" should work as well.

}

this.m_two = function() {
alert("m_two");
}
}
[...]

HTH

PointedEars
--
var bugRiddenCrashP ronePieceOfJunk = (
navigator.userA gent.indexOf('M SIE 5') != -1
&& navigator.userA gent.indexOf('M ac') != -1
) // Plone, register_functi on.js:16

[Thomas 'PointedEars' Lahn]

Thomas 'PointedEars' Lahn wrote:

As you can see, you cannot use a locally defined name in a string for
the window.setInter val() method (it would be the same with
window.setTimeo ut()). However, you can pass a Function object
reference, that is a reference to your method:

window.setInter val(this.m_two, 500);

Correction, use this instead to retain the method-object relationship:

window.setInter val(function callTwo() { this.m_two(); }, 500);
PointedEars
--
var bugRiddenCrashP ronePieceOfJunk = (
navigator.userA gent.indexOf('M SIE 5') != -1
&& navigator.userA gent.indexOf('M ac') != -1
) // Plone, register_functi on.js:16

[Richard Cornford]

Thomas 'PointedEars' Lahn wrote:

Thomas 'PointedEars' Lahn wrote:

>As you can see, you cannot use a locally defined name in a
string for the window.setInter val() method (it would be
the same with window.setTimeo ut()). However, you can
pass a Function object reference, that is a reference to
your method:

window.setInter val(this.m_two, 500);

Correction, use this instead to retain the method-object relationship:

window.setInter val(function callTwo() { this.m_two(); }, 500);

That is not going to help because when setInterval executes the function
expression (or the object resulting from the evaluation of the function
expression, to be precise) the - this - reference inside that function
will be to the global object and so - this.m_two - will have the same
meaning as when it was in the string in the earlier examples.

Richard.

[jamie.ly]

This function may help you. It is from the Prototype javascript
library. (http://prototypejs.org/api)

Function.protot ype.bind = function() {
var __method = this, args = arguments ? arguments : [], object =
args.shift();
return function() {
return __method.apply( object, args.concat(arg uments ? arguments :
[]));
}
}

After placing this before the code below you can do this and it should
work:

instead of : window.setInter val( "this.m_two ", 500 );
use: window.setInter val( this.m_two.bind ( this ), 500 );

What bind does is copies all of the methods and properties of 'this'
object into the m_two function as a new object. I've modified it a
bit, so if this doesn't work, just add the complete prototype library
from the site listed above.

[jamie.ly]

After placing this before the code below you can do this and it should
work:

instead of : window.setInter val( "this.m_two ", 500 );
use: window.setInter val( this.m_two.bind ( this ), 500 );

What bind does is copies all of the methods and properties of 'this'
object into the m_two function as a new object. I've modified it a
bit, so if this doesn't work, just add the complete prototype library
from the site listed above.

Alternatively, if you don't need to access any of the class's
properties in "m_two", just do what Thomas said above:

As you can see, you cannot use a locally defined name in a string for
the window.setInter val() method (it would be the same with
window.setTimeo ut()). However, you can pass a Function object
reference, that is a reference to your method:

window.setInter val(this.m_two, 500);

[Thomas 'PointedEars' Lahn]

Richard Cornford wrote:

Thomas 'PointedEars' Lahn wrote:

>Thomas 'PointedEars' Lahn wrote:

>> window.setInter val(this.m_two, 500);

Correction, use this instead to retain the method-object relationship:

window.setInter val(function callTwo() { this.m_two(); }, 500);

That is not going to help because when setInterval executes the function
expression (or the object resulting from the evaluation of the function
expression, to be precise) the - this - reference inside that function
will be to the global object and so - this.m_two - will have the same
meaning as when it was in the string in the earlier examples.

True, a closure is required:

this.m_one = function()
{
var me = this;
window.setInter val(function() { me.m_two(); }, 500);
};

this.m_two = function()
{
window.alert(th is.m_one);
};
PointedEars
--
Prototype.js was written by people who don't know javascript for people
who don't know javascript. People who don't know javascript are not the
best source of advice on designing systems that use javascript.
-- Richard Cornford, <f8************ *******@news.de mon.co.uk>

[Ralf Beutler]

Thomas 'PointedEars' Lahn schrieb:

Thomas 'PointedEars' Lahn wrote:

>As you can see, you cannot use a locally defined name in a string for
the window.setInter val() method (it would be the same with
window.setTime out()). However, you can pass a Function object
reference, that is a reference to your method:

window.setInter val(this.m_two, 500);

Correction, use this instead to retain the method-object relationship:

window.setInter val(function callTwo() { this.m_two(); }, 500);

You're wrong!

You definitely need closures for this, if you need access to this object:

function MyClass() {
//..
this.m_one = function() {
var me = this; // create a closure
this.interval = window.setInter val( function(){
me.m_two();
}, 1000 );
}
//..
}

br | rb
--
Sie freuten sich riesig, wenn eine Maschine nach sechs Stunden etwas
fertig brachte, wozu jeder Mensch auf der Straße für 2 Cent fähig
gewesen wäre. Anschließend ließen sie sich Bananen- und Sushi-Pizza
kommen und schliefen vor der Tastatur ein. [aus T.P., Heiße Hüpfer]

[Thomas 'PointedEars' Lahn]

ja******@gmail. com wrote:

Alternatively, if you don't need to access any of the class's
properties in "m_two", just do what Thomas said above:
[...]

*sigh* *There* *is* *no* *class*. My sig happens to be proved by your
statement.
PointedEars
--
Prototype.js was written by people who don't know javascript for people
who don't know javascript. People who don't know javascript are not the
best source of advice on designing systems that use javascript.
-- Richard Cornford, <f8************ *******@news.de mon.co.uk>

[Richard Cornford]

ja******@gmail. com wrote:

This function may help you. It is from the Prototype
javascript library. (http://prototypejs.org/api)

Function.protot ype.bind = function() {
var __method = this, args = arguments ? arguments : [], object =
args.shift();
return function() {
return __method.apply( object, args.concat(arg uments ? arguments :
[]));
}
}

You have got to be joking. That is far too bad even for Prototype.js
code. I know that they have long since broken compatibility with ECMA
262 3rd Ed. but that is not even going to work in common browser
environments.

And what do they think - args = arguments ? arguments : [] - is about?
The existence of an - arguments - object, and that the Identifier
'arguments' will refer to that object, is absolutely guaranteed (short
of jumping through some extreme hoops with things like -
with({arguments :null}){ args = arguments?argum ents:[];} -). And even
if - arguemtns - were allowed not exist the code would likely error out
at the first reference to it whenever it didn't. It would be difficult
to make this stuff up if you tried.

After placing this before the code below you can do this and
it should work:

instead of : window.setInter val( "this.m_two ", 500 );
use: window.setInter val( this.m_two.bind ( this ), 500 );

What bind does is copies all of the methods and properties of
'this' object into the m_two function as a new object.

No it does not, and if it did that would be a disaster in this context
(and very many others) as the copy would be a copy of the state of the
object at the time of the setInterval call and so the method would end
up acting on an object with a (potentially) out-of-date state, and if it
needed to change the state of its object it would not be able to, but
instead would only change the state of the copy.

I've modified it a bit,

So what precisely did you modify? That is, how broken was it before you
started playing with it?

so if this doesn't work,

If? When it doesn't work! Opera may be the only browser where this does
work, and that is because of an ECMAScript bug in Opera.

just add the complete prototype library
from the site listed above.

Considering how utterly trivial the solution(s) to this problem is(are)
if you understand what you are doing, that has got to be one of the
worst suggestions possible.

Richard.