CODEWITHSUNDEEP
javascriptvariablesobject
user2844700
user2844700

Reputation: 3

Declare variable based on object value in javascript

Simple issue I ran up against today and can't seem to find a way around it, whatever the solution is it's something I've never learned so leaving me stumped.

For reasons I won't get into, I need to get a value from an object and use it as the name of a new variable. Will be looping through a ton of these so needs to be repeatable. For example from an object like so,

obj = {
    "name": "object101"
};

What I want to get out of that is a var declaration in such a way that object101 is the name of the new var,

"var object101 =  // stuff"

But "var obj.name = // stuff" is not working, the dot is not valid it seems.

I also tried putting the object101 into it's own var like, var name = obj.name;.

Which holds the content fine. But then I immediately saw the hilarious problem with going, var name = // stuff

It just redefines "name" and is not placing the content of name. It does render right when in a console log like console.log("var "+name+" = stuff"); which is pretty much exactly how I want it to write to the code, but having this issue in the real code with the var being redefined in this case.

So I feel like I am missing something very basic in how you can provide the name to declare a var. Maybe some very simple syntax thing I am missing, or perhaps there is a process out there which will dynamically make a var declaration name based on some other object. I've done my fair share of js and never seen var [complex syntax resulting in name] =, it's always quite simple.

But my searching has drawn a blank so far on this exact issue. Anyone able to enlighten me?

Upvotes: 0

Views: 144

Answers (2)

Michael Lorton
Michael Lorton

Reputation: 44386

Wow, you really don't want to do what you think you want to do, but here goes.

If you are operating in a browser and you want the variables to be in global scope, fortunately the global scope has a name: window.

You can just do this:

window[obj.name] = 'stuff';

If you want it in in local scope, you can use the almost-forbidden keyword with:

var f = function(obj, b) {
  var fake_scope = {};
  with (fake_scope) {
    fake_scope[obj.name] = b;
    console.log(d);
  }
}

f( { name : 'd' } , 3 )

will print out 3.

If you need local scope and you don't want to use with, you will have to screw around with eval.

But seriously, if you do this, remember.

Upvotes: 2

sabof
sabof

Reputation: 8192

Well, in the interest of science:

(function() {
  var dynaVarName = 'testName';
  eval('var ' + dynaVarName + ';');
  eval(dynaVarName + ' = 5;');
  eval('console.log(' + dynaVarName + ');');  // => 5
}());

testName // => ReferenceError

So yes, you actually can create a local variable with a name based on an expression. I can't imagine the benefits of doing this though.

Upvotes: 1

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