How do I unset a variable, array element or object property in JavaScript?

jgivoni,

I haven't found a way to declaratively remove a variable as you're describing. When it comes to javascript, I try to stick with local variables so I don't get "unexpected" results if I want to use the same variable name in a different scope.

It may just require you to change the scope of the variables to prevent the problems you're having.

Ric

No, that's actually not my problem.
For instance, I am looping through an array with named elements (properties...?) and doing something to each of them.
I want to remove some elements from it before doing that.

But luckily I found the answer myself:

delete

You can:
delete x // Removes the variable x
delete x[i] // Removes the element with index i from array x
delete x.p // Removes the property p from object / array x

Quite simple - and works in IE and FF - but so strange that so relatively few seems to know of this.

Makes sense...I guess I didn't quite understand what you were trying to accomplish from your original submission.

I'm glad you found a workable answer!

Ric

Thanks for the input anyway :-)

I have to correct my previous answer though, as the transition from theory to praxis once again proved quirky.
I tried to remove a variable or object with the 'delete x' statement, but nothing happened. I didn't get a warning nor error message and the variable continued to exist with the same value!

It seems to work with properties and array elements though. The deleted property / element will have the value 'null' and 'undefined' if tested afterwards. (Meaning that both 'x.y == null' and 'x.y === undefined' evaluates to true after 'delete x.y')

Jakob

you can delete only implicitly declared variables, i.e.

var x=1; delete x; //false
y=2; delete y; // true

see http://developer.mozilla.org/en/docs/Cor...

however, length property of array is not affected, i.e:
color= new Array("red","green","blue");
delete color[2]; //"green" is deleted and no longer exists in color
alert(color.length); // !! 3 !!

Thanks, Janturon, that was quite helpful.

color = new Array("red", "green", "blue");
color.splice(1, 2); // deletes 2 elements from index 1 (leaving "red" in the array)

To unset a variable, array element or object property, use the "delete" keyword.

delete x[i] // Removes the element with index i from array x
delete x.p // Removes the property p from object / array x

var x=1; delete x; // Doesn't work
y=2; delete y; // Works

However, be careful when testing the lenght property of an array after deleting an element this way; i.e:

color = new Array("red","green","blue");
delete color[2]; // "green" is deleted and no longer exists in color
alert(color.length); // Still reports 3!!

Thanks,
Jakob

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use splice for arrays and delete for associative arrays

var x = new Array();
....
x.splice(....

Regards,
Alex

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simple:

var x = new Array();
x[0]="text0";
//x[1], x[2]...
x[100]="text100";

x="";

alert(x[100]);

Result-> undefined

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/**
* This variable provides way to verify any variable is undefined. The easiest
* way to do that is:
*
*  if (typeof(varname) == CONSTANT_UNDEFINED_DO_NOT_SET) {
*   alert('varname is undefined');
*  }
*
*
* NOTE: Do not pass variable to function, as undefined are simply not sent to
* functions.
*/
var CONSTANT_UNDEFINED_DO_NOT_SET;

/**
* Convenient method that can be called to verify the constant that is meant to
* be used verifying variables are undefined is, in fact, undefined. It is
* possible a Javascript can set this, so it becomes undefined.
*
* NOTE: this function will delete this variable so it is undefined again.
*
* @return
*/
function checkUndefinedConstant() {
 var result = typeof(CONSTANT_UNDEFINED_DO_NOT_SET) == 'undefined';
 if (!result) {
  var newUndefinedVarForSetting;
  CONSTANT_UNDEFINED_DO_NOT_SET = newUndefinedVarForSetting;
 }
 return result;
}

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