What is the process for removing a variable?

Question

What is the process for removing a variable?

Here is the issue with my JavaScript code - I am trying to delete the variable "code" so that it becomes undefined.

var code = $(this).data('code');
var userelm = $(this);

Below is the part where I try to achieve this:

if($('.code-1').val()!='' && $('.code-2').val()!='' && $('.code-3').val()!=''){
    if(code==$('.code-1').val()+$('.code-2').val()+$('.code-3').val()){
        $('.overlay').remove();
        $('.code-box').remove();
        $('.close-lock').remove();
        userelm.ajaxloader(); //custom function
        userelm.off();
        delete code;
        console.log(code);
        delete userelm;
    }
}

I'm puzzled as to why the code variable does not get removed and still retains a value instead of being set to undefined.

javascript

Answer 1

Answer №1

Removing a Variable in JavaScript:

Summary:

If you're struggling with deleting a variable in JavaScript, it's because JavaScript doesn't make it easy. The var command creates variables that cannot be deleted easily unless you resort to some advanced techniques.

The delete command is meant for properties of objects that weren't created using var.

JavaScript allows deletion of a variable created with var under specific conditions:

You're using a JavaScript interpreter or command line.
You're utilizing eval and creating/deleting the var within there.

To see a demonstration on the terminal, use the delete boo or delete(boo) commands. A demo using the js command line terminal can successfully delete a variable.

el@defiant ~ $ js

js> typeof boo
"undefined"

js> boo
typein:2: ReferenceError: boo is not defined

js> boo=5
5

js> typeof boo
"number"

js> delete(boo)
true

js> typeof boo
"undefined"

js> boo
typein:7: ReferenceError: boo is not defined

If you absolutely need to set your variable to undefined in JavaScript, here's one method:

In a JavaScript page, include this in myjs.html:

<html>
<body>
    <script type="text/JavaScript">
        document.write("aliens: " + aliens + "<br>");
        document.write("typeof aliens: " + (typeof aliens) + "<br>");
        var aliens = "scramble the nimitz";
        document.write("found some aliens: " + (typeof aliens) + "<br>");
        document.write("not saying it's aliens but... " + aliens + "<br>");
        aliens = undefined;
        document.write("aliens set to undefined<br>");
        document.write("typeof aliens: " + (typeof aliens) + "<br>");
        document.write("you sure they are gone? " + aliens);
    </script>
</body>
</html>

Upon opening myjs.html in a browser, it will display:

aliens: undefined
typeof aliens: undefined
found some aliens: string
not saying it's aliens but... scramble the nimitz
aliens set to undefined
typeof aliens: undefined
you sure they are gone? undefined

Warning: Setting a variable to undefined essentially assigns it to another variable. If someone tampers with undefined by running undefined = 'gotcha!', then setting your variable to undefined will result in: "gotcha!".

How to Determine if a Variable has No Value:

Instead of using undefined, consider using null like this:

document.write("skittles: " + skittles + "<br>");
document.write("typeof skittles: " + (typeof skittles) + "<br>");
var skittles = 5;
document.write("skittles: " + skittles + "<br>");
document.write("typeof skittles:" + typeof skittles + "<br>");
skittles = null;
document.write("skittles: " + skittles + "<br>");
document.write("typeof skittles: " + typeof skittles);

This code snippet results in:

skittles: undefined
typeof skittles: undefined
skittles: 5
typeof skittles:number
skittles: null
typeof skittles: object

If you're not using strict mode, you can delete variables created in this manner:

<script type="text/JavaScript">
   //use strict
   a = 5;
   document.writeln(typeof a);        //prints number
   delete a;
   document.writeln(typeof a);        //prints undefined
</script>

However, uncommenting use strict will prevent this JavaScript code from executing.

Answer 2

Removing a Variable in JavaScript:

Summary:

If you're struggling with deleting a variable in JavaScript, it's because JavaScript doesn't make it easy. The var command creates variables that cannot be deleted easily unless you resort to some advanced techniques.

The delete command is meant for properties of objects that weren't created using var.

JavaScript allows deletion of a variable created with var under specific conditions:

You're using a JavaScript interpreter or command line.
You're utilizing eval and creating/deleting the var within there.

To see a demonstration on the terminal, use the delete boo or delete(boo) commands. A demo using the js command line terminal can successfully delete a variable.

el@defiant ~ $ js

js> typeof boo
"undefined"

js> boo
typein:2: ReferenceError: boo is not defined

js> boo=5
5

js> typeof boo
"number"

js> delete(boo)
true

js> typeof boo
"undefined"

js> boo
typein:7: ReferenceError: boo is not defined

If you absolutely need to set your variable to undefined in JavaScript, here's one method:

In a JavaScript page, include this in myjs.html:

<html>
<body>
    <script type="text/JavaScript">
        document.write("aliens: " + aliens + "<br>");
        document.write("typeof aliens: " + (typeof aliens) + "<br>");
        var aliens = "scramble the nimitz";
        document.write("found some aliens: " + (typeof aliens) + "<br>");
        document.write("not saying it's aliens but... " + aliens + "<br>");
        aliens = undefined;
        document.write("aliens set to undefined<br>");
        document.write("typeof aliens: " + (typeof aliens) + "<br>");
        document.write("you sure they are gone? " + aliens);
    </script>
</body>
</html>

Upon opening myjs.html in a browser, it will display:

aliens: undefined
typeof aliens: undefined
found some aliens: string
not saying it's aliens but... scramble the nimitz
aliens set to undefined
typeof aliens: undefined
you sure they are gone? undefined

Warning: Setting a variable to undefined essentially assigns it to another variable. If someone tampers with undefined by running undefined = 'gotcha!', then setting your variable to undefined will result in: "gotcha!".

How to Determine if a Variable has No Value:

Instead of using undefined, consider using null like this:

document.write("skittles: " + skittles + "<br>");
document.write("typeof skittles: " + (typeof skittles) + "<br>");
var skittles = 5;
document.write("skittles: " + skittles + "<br>");
document.write("typeof skittles:" + typeof skittles + "<br>");
skittles = null;
document.write("skittles: " + skittles + "<br>");
document.write("typeof skittles: " + typeof skittles);

This code snippet results in:

skittles: undefined
typeof skittles: undefined
skittles: 5
typeof skittles:number
skittles: null
typeof skittles: object

If you're not using strict mode, you can delete variables created in this manner:

<script type="text/JavaScript">
   //use strict
   a = 5;
   document.writeln(typeof a);        //prints number
   delete a;
   document.writeln(typeof a);        //prints undefined
</script>

However, uncommenting use strict will prevent this JavaScript code from executing.

Answer 3

Answer №2

The delete operation doesn't actually remove a variable.

When using the delete operator, it specifically removes a property from an object.

One possible alternative is:

variable = null;

Answer 4

The delete operation doesn't actually remove a variable.

When using the delete operator, it specifically removes a property from an object.

One possible alternative is:

variable = null;

Answer 5

Answer №3

Strict mode can also be applied in the following example:

"use strict";

var bar = 2;
console.log(bar);
// 2

bar = (function() {}());
console.log(bar);
// undefined

:D

Answer 6

Strict mode can also be applied in the following example:

"use strict";

var bar = 2;
console.log(bar);
// 2

bar = (function() {}());
console.log(bar);
// undefined

:D

Answer 7

Answer №4

To implement this in the overall context, consider the following:

var y = 5;
delete window.y;

Answer 8

To implement this in the overall context, consider the following:

var y = 5;
delete window.y;

Answer 9

Answer №5

Removing items with the delete keyword does not impact variable names

Visit this link for more information on the delete operator in JavaScript.

a = 50;         // assigns 50 to variable a
let b = 60;      // declares a new variable, b
myVariable = {
  m: 7,
  n: 8
};

delete a;        // returns true (a is a property of the global object that can be deleted)
delete b;        // returns false (variables are not affected by delete operation)
delete Math.E;   // returns false (certain predefined properties cannot be deleted)
delete myVariable.m; // returns true (user-defined properties can be removed)

delete myVariable;   // returns true (myVariable is a property of the global object and can be deleted)

Answer 10

Removing items with the delete keyword does not impact variable names

Visit this link for more information on the delete operator in JavaScript.

a = 50;         // assigns 50 to variable a
let b = 60;      // declares a new variable, b
myVariable = {
  m: 7,
  n: 8
};

delete a;        // returns true (a is a property of the global object that can be deleted)
delete b;        // returns false (variables are not affected by delete operation)
delete Math.E;   // returns false (certain predefined properties cannot be deleted)
delete myVariable.m; // returns true (user-defined properties can be removed)

delete myVariable;   // returns true (myVariable is a property of the global object and can be deleted)

Answer 11

Answer №6

The answer provided by others is both simple and effective

code = null;
code = undefined;

However, I would like to explain why the statement delete code; does not work as expected

The delete keyword is designed to delete properties of objects specifically, not variables.

var obj = {
  'first' : 10;
}
//This will print
console.log(obj.first)

delete obj.first;

//This will result in either undefined/null or an error
console.log(obj.first)

Bonus tip for developers:

var item = 10;
delete item;
//This will print 
console.log(item);

//Explanation: When a variable is declared with var, it is of primitive data type and cannot be deleted.


item = 10;
delete item;
//This will result in a reference error
console.log(item);

//Explanation: When a variable is declared without var, it becomes a property of the global 'window' object and can be deleted.

Answer 12

The answer provided by others is both simple and effective

code = null;
code = undefined;

However, I would like to explain why the statement delete code; does not work as expected

The delete keyword is designed to delete properties of objects specifically, not variables.

var obj = {
  'first' : 10;
}
//This will print
console.log(obj.first)

delete obj.first;

//This will result in either undefined/null or an error
console.log(obj.first)

Bonus tip for developers:

var item = 10;
delete item;
//This will print 
console.log(item);

//Explanation: When a variable is declared with var, it is of primitive data type and cannot be deleted.


item = 10;
delete item;
//This will result in a reference error
console.log(item);

//Explanation: When a variable is declared without var, it becomes a property of the global 'window' object and can be deleted.

Answer 13

Answer №7

When variables are generated dynamically, they will be cleared automatically once there are no longer any references to them.

(function(){
  var b = 2;
})(); //b remains accessible until this point

Answer 14

When variables are generated dynamically, they will be cleared automatically once there are no longer any references to them.

(function(){
  var b = 2;
})(); //b remains accessible until this point

Answer 15

Answer №8

the reason is because when you use var to define a variable, you cannot delete it later on. Instead, you should do this:

userelm = null;

Alternatively, you can simply omit using var. Check out this question for more details: How to unset or remove a Javascript variable?

Answer 16

the reason is because when you use var to define a variable, you cannot delete it later on. Instead, you should do this:

userelm = null;

Alternatively, you can simply omit using var. Check out this question for more details: How to unset or remove a Javascript variable?

Answer 17

Answer №9

There's no need to remove the var if it's declared within a function - once the function ends, the inner var ceases to exist. It's best practice not to declare variables globally in order to avoid potential issues.

Answer 18

There's no need to remove the var if it's declared within a function - once the function ends, the inner var ceases to exist. It's best practice not to declare variables globally in order to avoid potential issues.

Answer 19

Answer №10

Setting myvariable = null did not yield the desired results.

However, assigning myvariable = function(){}; proved to be successful.

Answer 20

Setting myvariable = null did not yield the desired results.

However, assigning myvariable = function(){}; proved to be successful.

What is the process for removing a variable?

Answer №1

Removing a Variable in JavaScript:

How to Determine if a Variable has No Value:

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

Answer №7

Answer №8

Answer №9

Answer №10

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