Question

I have an object in Javascript:

function MyObject(aField) {
    this.field = aField;
}

MyObject.prototype.aFunction = function() {
    return this.field;
}

Then

var anInstance = new MyObject("blah");
var s = anInstance.aFunction();

this works fine, but if I pass the function to another function:

callLater(anInstance.aFunction);

I don’t control callLater and it’s minified, but it seems that it’s calling aFunction using call() or apply(). Therefore, this points to another object and field is undefined.

What’s the best practice to avoid this situation I’m facing?

Answer 1

That’s because you lost the value of this Try this instead:

callLater(function() { anInstance.aFunction() });

Explaination, Think of it this way

function MyObject(aField) {
    this.field = aField;
}
function MyObject2(aField) {
    this.field = aField;
}
MyObject.prototype.aFunction = someFunct;
MyObject2.prototype.aFunction = someFunct;

Now what does someFunct belong to?

Well try doing MyObject.prototype.aFunction === MyObject2.prototype.aFunction it’ll be true!

You see the problem Therefore it needs to be called from the class and not just referenced by value.