Home  >  Article  >  Web Front-end  >  What does javascript:void mean?

What does javascript:void mean?

藏色散人
藏色散人Original
2021-03-05 14:22:4317005browse

javascript:void is a usage format of the void operator in Javascript; the void operator specifies to calculate an expression but does not return a value; developers can use void to prevent a tag from jumping when clicked , you can also use void0 to take undefined.

What does javascript:void mean?

The operating environment of this article: windows7 system, javascript version 1.8.5, Dell G3 computer.

void in Javascript is an operator that specifies to evaluate an expression but not return a value. You can use void to prevent the a tag from jumping when clicked. You can also use void0 to take undefined.

void Operator Usage

javascript:void (expression)
javascript:void expression

expression is a Javascript standard expression to be evaluated. The parentheses outside the expression are optional, but are a good practice to write.

You can use the void operator to specify a hyperlink. The expression will be evaluated but nothing will be loaded into the current document. The above code creates a hyperlink and nothing happens to the user later. Nothing happens on Javascript when the user links.

Description in the ECMAScript 262 specification

The void Operator
The production UnaryExpression : void UnaryExpression is evaluated as follows:
Let expr be the result of evaluating UnaryExpression.
Call GetValue(expr).
Return undefined.
NOTE: GetValue must be called even though its value is not used because it may have 
observable side-effects.

It can be understood from the specification that no matter what the expression after void is, the void operator will return undefined

[Recommended learning: js basic tutorial]

Why use void

undefined is not a reserved word or keyword in Javascript

function isUndefined(param) {
    let undefined = 'hello world';    
    return undefined === param;
}

We can define a variable called undefined in the context of a function. At this time, if we want to access the real undefined, we can only access undefined through the global scope.

window.undefined;
GLOBAL.undefined;

Unfortunately, window and GLOBAL can still be defined in a function context, so taking undefined from them is not a safe and reliable method

function test() {    let 
        undefined = 'hello world',        
        window = { undefined: 'joke' },
        f = {}
    ;    
        console.log(undefined);    
        console.log(window.undefined);    
        console.log(f.a === undefined);    
        console.log(f.a === void 0);
}

Judge undefined

function isUndefined(param) { 
   return param === void 0;
}
另外一种方式
function getUndefined() {
    return;
};
    function isUndefined(param) {    
    return param === getUndefined();
}

This method is feasible because a function that does not specify a return value will By default, undefined is returned. The disadvantage is that in order to determine undefined, a function must be declared, which will cause a loss in performance.

Priority

void Priority is second only to. [] ()

Summary:

It is safer to use void 0 to get undefined than to use literal undefined. Void 0 should be used first.

Fill in the href of 3499910bf9dac5ae3c52d5ede7383485 to ensure that no page jump occurs when clicked. Avoid adding click events to the a tag and use return false to organize the default behavior.

The above is the detailed content of What does javascript:void mean?. For more information, please follow other related articles on the PHP Chinese website!

Statement:
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn