Is it possible in JavaScript to define a variable name with a function parameter?

Here is my jsFiddle. In the example below, I would like varB to be defined as null when it is passed through makeNull(varName):

var varA = undefined;
if (varA == undefined) {
  varA = null;
}
var varB = undefined;

makeNull(varB);

function makeNull(varName) {
  if (varName == undefined) {
    varName = null;   
  }
}  

alert (varA + ' | ' + varB);

​

Is it possible in JavaScript to define a variable name with a function parameter?

Here is my jsFiddle. In the example below, I would like varB to be defined as null when it is passed through makeNull(varName):

var varA = undefined;
if (varA == undefined) {
  varA = null;
}
var varB = undefined;

makeNull(varB);

function makeNull(varName) {
  if (varName == undefined) {
    varName = null;   
  }
}  

alert (varA + ' | ' + varB);

​

• javascript
• function
• variables
• naming-conventions
• function-parameter

Share Improve this question Follow asked Oct 2, 2012 at 14:59 Mark RummelMark Rummel 2,9501010 gold badges3838 silver badges5252 bronze badges 4

• You appear to be trying to break encapsulation by changing the bindings in another higher scope. Why? Even if there is a solution, this isn't good software practice. – Francis Avila Commented Oct 2, 2012 at 15:01
• I agree with Francis, but there's nothing wrong with creating functions to modify objects or variables. You should just be explicit about what you pass in, and what you return. Maybe something like this? jsfiddle/zVM9M/2 – Daniel Attfield Commented Oct 2, 2012 at 15:02
• @FrancisAvila I'm getting the value of multiple checkboxes via jQuery. The ones that are checked = 1 the ones that aren't checked are undefined, but I need them to be null. For example: checkbox1 = 1, checkbox2 = 1, checkbox3 = null. – Mark Rummel Commented Oct 2, 2012 at 15:21
• 1 If you represent all the checkboxes as an array, you can pass the entire array to your makeNull function, and it can set the undefined elements to null. – Barmar Commented Oct 2, 2012 at 16:27

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3 Answers 3

Sorted by: Reset to default 2

If you are trying to define a variable with a function parameter then you either want to use an array or an object.

JavaScript doesn't provide "call by reference" parameters. When you call a function, it receives the values of the argument expressions, not references to the variables that were in the expressions. So it can't modify the bindings of those variables.

If you want to do something like this, you can use containers and labels, e.g.

function makeNull(obj, label) {
  if (obj[label] === undefined) {
      obj[label] = null;
  }
}
var varB = { abc: undefined }
makeNull(varB, 'abc');

you can pass a variable (defined as 'undefined') to a function and set its value.

http://jsfiddle/AwnVN/