void
operator
评估给定
expression
然后返回
undefined
.
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void expression
This operator allows evaluating expressions that produce a value into places where an expression that evaluates to
undefined
is desired.
void
operator is often used merely to obtain the
undefined
primitive value, usually using "
void(0)
" (which is equivalent to "
void 0
"). In these cases, the global variable
undefined
can be used.
It should be noted that
the precedence
of the
void
operator should be taken into account and that parentheses can help clarify the resolution of the expression following the
void
运算符：
void 2 == '2'; // (void 2) == '2', returns false void (2 == '2'); // void (2 == '2'), returns undefined
当使用
立即援引函数表达式
,
void
can be used to force the
function
keyword to be treated as an expression instead of a declaration.
void function iife() {
console.log("Executed!");
}();
// Output: "Executed!"
Executing the above function without the
void
keyword will result in an
Uncaught SyntaxError
.
When a browser follows a
javascript:
URI, it evaluates the code in the URI and then replaces the contents of the page with the returned value, unless the returned value is
undefined
。
void
operator can be used to return
undefined
。例如：
<a href="javascript:void(0);"> Click here to do nothing </a> <a href="javascript:void(document.body.style.backgroundColor='green');"> Click here for green background </a>
注意
:
javascript:
pseudo protocol is discouraged over other alternatives, such as unobtrusive event handlers.
Arrow functions introduce a short-hand braceless syntax that returns an expression. This can cause unintended side effects by returning the result of a function call that previously returned nothing. To be safe, when the return value of a function is not intended to be used, it can be passed to the void operator to ensure that (for example) changing APIs do not cause arrow functions' behaviors to change.
button.onclick = () => void doSomething();
This ensures the return value of
doSomething
changing from
undefined
to
true
will not change the behavior of this code.
| 规范 |
|---|
|
ECMAScript (ECMA-262)
The definition of 'The void Operator' in that specification. |
| Desktop | Mobile | Server | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
void
|
Chrome 1 | Edge 12 | Firefox 1 | IE 5 | Opera 4 | Safari 3.2 | WebView Android 1 | Chrome Android 18 | Firefox Android 4 | Opera Android 10.1 | Safari iOS 3 | Samsung Internet Android 1.0 | nodejs 0.1.100 |
完整支持