What is void and when to use void type in JavaScript ?
Last Updated :
31 Dec, 2021
In this article, we will know what is void operator in Javascript, along with discussing the particular condition where void operator can be used & understanding their implementation through the examples.
The void keyword in JavaScript, is used to evaluate an expression which does not return any value. The void operator is an unary operator that accepts the single operand, which may be of any type. The importance of the void keyword come into role when we just need to evaluate an expression instead of returning its value. It means, by using it, we can prevent the browser from displaying the result of the execution of the expression.
Syntax:
void expression
void(expression)
The void operator has an operator precedence ie., the priority will be given to operators while parsing a statement that has more than one operator performing operations in it. Here, we have used the parenthesis, to express the purpose of the expression, according to its precedence.
For instance, consider the below example:
void (10 == '10') // undefined
void 10 == '10' // false
For the 1st case, when the number is compared with string, inside the parenthesis with the void keyword, it returns undefined whereas in the 2nd case, when the expression is evaluates directly with the void keyword, it returns false.
Example: This example describes the returning undefined value.
HTML
<script>
function foo() {
return void 0;
}
console.log(foo());
</script>
|
Output:
undefined
void 0 can be used as a placeholder URL that represents an onclick event is tied to the link to perform the actual action. The void 0 is also commonly used in code downsizing, as it is a way of writing undefined.
There are 3 instances where the void operator can be used:
Active Javascript URLs: The javascript: is referred to as the pseudo URL, when we provide it as a value of “href” in an anchor tag, the browser evaluates the expression that follows the “:” symbol. On the other hand, the expression that follows the “:” is usually used as a referenced path.
The void operator is most commonly used in managing the javascript: URL (s) because it allows the browser to show the end result of the evaluation of the expression rather than the returned value of the evaluated expression on the client side.
Example: In this example, the link changes the color of the background to green without returning any value to the browser.
HTML
<!DOCTYPE html>
<html>
<head>
<title>Using Void in URLs</title>
</head>
<body>
<a href=
"javascript:void(document.body.style.backgroundColor='#32CD32');">
Click here to change the background color.
</a>
</body>
</html>
|
Output:
Inactive Javascript URLs: In some cases, it is not required by a link to navigate anywhere or do anything. To achieve it, we combine the pseudo URL (javascript:) with void(0) as a value of an href, it tells the browser to return/do nothing when that link is clicked.
Example: This example explains the generating the inactive Javascript URL.
HTML
<html>
<head>
<title>Creating Inactive URL</title>
</head>
<body>
<pre>
Syntax to make Inactive Javascript URLs:
<a href="javascript:void(0)">Click here to do nothing.</a>
</pre>
</body>
</html>
|
Output: The link will be recognized by the browser but the link doesn’t react at all. When 0 is passed to void as an argument, it does nothing or returns nothing. Here “Click here and do nothing” link doesn’t do anything at all, as depicted in the output.
Suppression of Arrow Functions: Arrow functions provide a braceless syntax to return the value of an expression. To ensure that the return value of the function expression (when it is of no use) doesn’t affect the code in any way, it can be passed into a void operator.
Example: This example explains the returning the value of an expression.
HTML
<html>
<head>
<title>Returning the value of an expression</title>
</head>
<body>
<h3>Here we see how we can return undefined value on purpose:</h3>
<script>
function someOtherFunction(num) {
return num + 1
}
const toReturnUndefined = () => void someOtherFunction(1);
console.log(toReturnUndefined());
</script>
</body>
</html>
|
Output:
Returning Undefined Value on Purpose: We can convert any variable’s value to an undefined type.
HTML
<html>
<head>
<title>Returning Undefined Value on Purpose</title>
</head>
<body>
<h3>Click the following to Return the Undefined Value:</h3>
<input type="button"
value="Click Me"
onclick="genUValue();" />
<script>
function genUValue() {
var g, f, h;
g = void(f = 13, h = 19);
document.write('g = ' + g);
}
</script>
</body>
</html>
|
Output:
Immediately Invoked Function Expression: An Immediately Invoked Function Expression(IIFE) is a type of Javascript function which gets executed as soon as it gets defined. They are very useful because they don’t affect the global object and the remote variable declarations very easily. We can use the void operator to create IIFEs. It will force the function to be treated as an expression rather than a declaration.
Example:
HTML
<html>
<head>
<title>Creating a IIFE Using the Void operator</title>
</head>
<body>
<h3>Here we are creating a IIFE Using the Void operator:</h3>
<script>
void function iife() {
console.log("IIFE is made with void operator");
}();
iife();
</script>
</body>
</html>
|
Output:
Similar Reads
What is any type, and when to use it in TypeScript ?
Any is a data type in TypeScript. Any type is used when we deal with third-party programs and expect any variable but we don't know the exact type of variable. Any data type is used because it helps in opt-in and opt-out of type checking during compilation. In this article, we will see what is any T
3 min read
What is the use of TypedArray Object in JavaScript ?
Introduction: Arrays in Java and C++ are data structures, that are of fixed-size contiguous and store homogeneous data. These arrays utilize contiguousness and caching to improve performance thus reducing the random access time. However, JavaScript arrays are different beasts. Unlike typical arrays,
4 min read
What is an unknown type and when to use it in TypeScript ?
In Typescript, any value can be assigned to unknown, but without a type assertion, unknown can't be assigned to anything but itself and any. Similarly, no operations on an unknown are allowed without first asserting or restricting it down to a more precise type. similar to any, we can assign any val
3 min read
What is Variable Scope in JavaScript ?
Variable scope is the context of the program in which it can be accessed. In programming, a variable is a named storage location that holds data or a value. Think of it as a container that you can use to store and manipulate information in your code. Variables allow you to work with data in a flexib
4 min read
Check if a Variable is of Function Type using JavaScript
A function in JavaScript is a set of statements used to perform a specific task. A function can be either a named one or an anonymous one. The set of statements inside a function is executed when the function is invoked or called. [GFGTABS] javascript let gfg = function(){/* A set of statements */};
3 min read
How to Use JavaScript: void(0) and onClick?
Using javascript:void(0) in combination with the onClick attribute is a technique used in HTML to create links or clickable elements that perform actions without navigating away from the page. This is common when you want to attach a JavaScript function or event handler to a clickable element but pr
2 min read
What is the practical use for a closure in JavaScript?
In JavaScript, closures are defined as inner functions that have access to variables and parameters of outer function even after the outer function has returned. The below examples show the practical use of closures: Example: In this example, a variable mult is defined that is local to the function
2 min read
What is spread, default and rest parameters in JavaScript ?
The default, spread, and rest parameters were added in ES6. Default Parameter: It is used to give the default values to the arguments, if no parameter is provided in the function call. Syntax: function fnName(param1 = defaultValue1, ..., paramN = defaultValueN) { ... } Example 1: In the below exampl
2 min read
When should we use double or single quotes in JavaScript ?
This article aims to clarify when you should use double or single quotes while coding in JavaScript. If you have worked with JavaScript, you may know that it allows expressing string literals with both double quotes (“) and single quotes (‘). There are many differences between double and single quot
3 min read
What does javascript:void(0) mean?
javascript:void(0) is commonly used in HTML to create a link that doesn’t perform any action or navigate to a new page. When placed in the href attribute of an <a> tag, it allows the link to execute JavaScript code without reloading or changing the current page. This is particularly useful for
4 min read