是“(function(){})()”和“(function(){}())”在JavaScript中功能相同? [英] Are "(function ( ) { } ) ( )" and "(function ( ) { } ( ) )" functionally equal in JavaScript?
问题描述
下面的这两个代码块警告 foo
然后})()
和}())
。
代码1:
(function()
{
bar ='bar' ;
alert('foo');
})();
alert(bar);
代码2:
(function()
{
bar ='bar';
alert('foo');
}());
alert(bar);
所以除了语法之外,还有什么区别?
不;它们是相同的
但是,如果您事先添加 new
.something
之后,它们会有所不同。
代码1
new(function(){
this.prop = 4;
})().prop;
此代码创建此函数类的新实例,然后获取 prop
新实例的属性。
它返回 4
。
它相当于
函数MyClass(){
this.prop = 4;
}
new MyClass()。prop;
代码2
new(function(){
return {Class:function(){}};
}()).Class;
这段代码在<$ $上调用 new
c $ c> Class 属性。
由于函数调用的圆括号位于外部圆括号内,所以它们不会被新的
表达式,而是通常调用函数,返回它的返回值。
new
表达式解析为 .Class
并实例化。 ( new
之后的括号是可选的)
它相当于
var namespace = {Class:function(){}};
函数getNamespace(){return namespace; }
new(getNamespace()).Class;
//或者,
new namespace.Class;
如果调用 getNamespace()
,这将被解析为(new getNamespace())。Class
—它会调用实例化 getNamespace
类并返回新实例的 Class
属性。
Both of these code blocks below alert foo
then bar
. The only difference is })()
and }())
.
Code 1:
(function()
{
bar = 'bar';
alert('foo');
})();
alert(bar);
Code 2:
(function()
{
bar = 'bar';
alert('foo');
}());
alert(bar);
So is there any difference, apart from the syntax?
No; they are identical
However, if you add new
beforehand and .something
afterwards, they will be different.
Code 1
new (function() {
this.prop = 4;
}) ().prop;
This code creates a new instance of this function's class, then gets the prop
property of the new instance.
It returns 4
.
It's equivalent to
function MyClass() {
this.prop = 4;
}
new MyClass().prop;
Code 2
new ( function() {
return { Class: function() { } };
}() ).Class;
This code calls new
on the Class
property.
Since the parentheses for the function call are inside the outer set of parentheses, they aren't picked up by the new
expression, and instead call the function normally, returning its return value.
The new
expression parses up to the .Class
and instantiates that. (the parentheses after new
are optional)
It's equivalent to
var namespace = { Class: function() { } };
function getNamespace() { return namespace; }
new ( getNamespace() ).Class;
//Or,
new namespace.Class;
Without the parentheses around the call to getNamespace()
, this would be parsed as (new getNamespace()).Class
— it would call instantiate the getNamespace
class and return the Class
property of the new instance.
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