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Here is something weird, and I don't know how to overcome it.

Basically, I have this string here:

var s = 'var Bla = {variable: true, get: function() { return this.variable;}}; return Bla;'

and using the Function constructor to parse this construct.

var fn = new Function(s);

It works great, except that the inside function 'get' is no longer there .. like it didn't got parsed?! 

fn().variable  -> is there and returns "true".
fn().get  -> is undefined, not existing.

Any ideas?

PS: I edited my original question to indicate what's really missing.

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7
  • Because you aren't passing a function to the function constructor. Commented Nov 20, 2014 at 21:52
  • I wonder if you are running into the getter syntax. You could try changing the name of that property. Commented Nov 20, 2014 at 21:52
  • 2
    @Brennan - they're passing a function body to the constructor which is allowed. Commented Nov 20, 2014 at 21:53
  • Ah, thanks, was not aware of that Commented Nov 20, 2014 at 21:55
  • Btw - eval the same issue. @Brennan: new Function is the function constructor. Check developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… Commented Nov 20, 2014 at 21:56

2 Answers 2

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4

The code you've posted is the equivalent of this:

var fn = function() {
    var Bla = {
        variable: true, 
        get: function() { 
            return this.variable;
        }
    };
    return Bla;
}

So you can't directly use fn.variable or fn.get - instead you need to call that function:

var x = fn();
alert(x.get()); //alerts true
x.variable = 1;
alert(x.get()); //alerts 1

Bla is just a local variable within the function, and doesn't get returned from it. The code could easily just have been:

var fn = function() {
    return {
        variable: true, 
        get: function() { 
            return this.variable;
        }
    };
}

And you'd get the same effect. After calling the function, the object returned from it is what contains variable and get:

example object

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3 Comments

Sorry I should have been more explicit. This works, however the .get is not part of the return object of Bla .. it's just not there.
@flyandi Can you explain more? Bla is just a local variable within the function and effectively ceases to exist as soon as the function returns. The object returned from the function certainly does contain both variable and get: imgur.com/VLm4b7y
I feel stupid right now .. I literally forgot the () on one of the callers of this routine within my library.. but it was the missing () that caused the issue :-) - Thanks everyone!
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Your example works fine.

I tried it and issuing:

fn().get()

returns true as you'd expect.

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4 Comments

@flyandi—any browser that supports ES5 (such as Chrome).
I did it in chrome. I opened the debugger and copy and pasted the 2 lines you have into the console. Then I issued: fn().get();
also fn().bla returns undefined as i'd expect. Your first post (edited I see) says you got something different? That doesn't make any sense. fn() will return the Bla object. That object has no property "bla".
Yeah I figured it out, I was missing the () from one of the sub modules which is using the raw constructor :-) .. I modified my post to reflect the correct property ("variable").

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