javascript - updating global object variables via a function

Question

Weird problem here, I'm trying to use a global function to update my settings object, example:

    var Settings = new Object;
    Settings.savepos = 'true';

    function UpdateSetting(obj,value){
        eval("Settings.obj = value");
        alert(Settings.savepos);
    }

The obj is the key of the object, meaning if I call the function with

UpdateSetting('savepos','false')

the alert will always just give me true, how do I convert that eval or any alternative so it will update settings object's key with the value?

Wolph · Accepted Answer · 2010-09-19 22:33:06Z

1

You are setting Settings.obj, not setting.savepos.

Try this instead:

function UpdateSetting(obj,value){
    Settings[obj] = value;
    alert(Settings.savepos);
};

answered Sep 19, 2010 at 22:33

Wolph

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Comments

crazy2be · Accepted Answer · 2010-09-19 23:00:47Z

You are always changing the "obj" key of the object to equal value, which is likely to be undefined (or, at least, not defined to what you want) in the context eval() executes it in. So, you have two options. First, you can keep using eval() (although i don't recommend it because it's more pain than necessary):

var Settings = new Object;
Settings.savepos = 'true';

function UpdateSetting(obj,value){
    eval("Settings."+obj+" = '"+value+"'");
    alert(Settings.savepos);
}

Or, as numerous other have suggested, you can use the array operator[] to access the property by key:

var Settings = new Object;
Settings.savepos = 'true';

function UpdateSetting(obj,value){
    Settings[obj] = value;
    alert(Settings.savepos);
}

vol7ron · Accepted Answer · 2010-09-20 02:27:50Z

1

you dont need an eval
you're setting .obj, not .savepos (there is no interpolation for the string)
you may be calling it wrong.

I'm not exactly sure why you don't just set the value directly (eg. Settings.savepos=false;).
You can attach the function to that object to do something similar:

var Settings            =  new Object;
Settings.savepos        =  true;
Settings.UpdateSetting  =  function (prop,value){this[prop] = value;}

Settings.UpdateSetting('savepos',false);

edited Sep 20, 2010 at 2:27

answered Sep 19, 2010 at 22:44

vol7ron

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2 Comments

vol7ron Over a year ago

If you were to have multiple Settings objects, then you should consider using the prototype method (google: 'javascript prototype method'). It's a little bit harder to search for it because there's also a 'prototype' JavaScript framework. Glad this helped :)

vol7ron Over a year ago

I wanted to note that I still encourage setting the value directly eg var prop = 'savepos'; Settings[prop] = true;, but I also know that people have their reasons for asking the question and wanting it to be done a certain way.

Jason McCreary · Accepted Answer · 2010-09-19 22:32:36Z

0

You should be able to use array notation on the object. Underneath it's just a keyed hash.

Try:

Settings[obj] = value;

I'd also suggest passing values as they are, i.e. string, int, etc:

UpdateSetting('key_name', false);

answered Sep 19, 2010 at 22:32

Jason McCreary

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1 Comment

Russ Cam Over a year ago

I believe the technical definition is subscript notation

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