Uncaught TypeError: Cannot set property 'xxx' of undefined

[The Little Guy]

I am trying to do oop javascript, but I am getting an error with this:

function JEffect(){
var props = new Array('x', 'y');
this.prototype.transition = function(obj, prop, begin, finish, drration){
	if(!this.in_array(prop, props)){
		alert('not found');
	}
}
var in_array = function(needle, haystack){
	for(var k in haystack){
		if(k == needle){
			return true;
		}
	}
	return false;
}
}

<script type="text/javascript">
var effect = new JEffect();
effect.transition('', 'm', 1, 2, 2);
</script>

 

The error message says:

Uncaught TypeError: Cannot set property 'transition' of undefined

 

What does that mean and what do I do?

[Alex]

You have a few problems there. You can't set properties through "this.prototype", and you don't define properties with "var" just use the this keyword.

 

This won't throw any errors, but I'm not entirely sure what you're attempting to do:

 

function JEffect(){
this.props = new Array('x', 'y');

this.in_array = function(needle, haystack){
	for(var k in haystack){
		if(k == needle){
			return true;
		}
	}
	return false;
}
}

JEffect.prototype.transition = function(obj, prop, begin, finish, drration){
if(!this.in_array(prop, this.props)){
	alert('not found');
}
}

var effect = new JEffect();
effect.transition('', 'm', 1, 2, 2);

 

Because you're adding the in_array method in the constructor I'm guessing you want to add that to the JEffect prototype as well, but I left it as you had it.

[The Little Guy]

Thanks!