Question

最近我遇到了一段像这样的代码：

var noop = function(){};
    options.ondragover = options.ondragover || noop;
    options.ondragleave = options.ondragleave || noop;
    options.ondrop = options.ondrop || noop;
    options.onfilesdone = options.onfilesdone || noop;

Answer 1

这是无操作功能

在以下链接中详细讨论

https://disqus.com/home/discussion/chrislaughlin/noop_no_operation_function/oldest/

What is the JavaScript convention for no operation?

Answer 2

您发布的代码声明了一个名为noop（No Operation）的空函数，作为在某些条件适用时执行的替代方法。例如代码：

ColPattern

检查FROM OPENXML (@hDoc, '/Transfer/Products/Product',2) WITH ( Identifier varchar(80), ProductItemCode varchar(10), SerialNumber varchar(48), NetWeight decimal(13,2), GrossWeight decimal(13,2), PackDate datetime 'Attribute[@Name = "PackDate"]', PlantID int 'Attribute[@Name = "PlantID"]', SlgrDate datetime 'Attribute[@Name = "SlgrDate"]' )是否存在，如果没有，则将空函数分配给变量。

Answer 3

它只是一个自我执行的函数，无论你声明什么，你都可以执行相同的操作。

它限制范围并将其设为私有并隐藏全局对象中的变量。

// Somewhere it is defined as global..
var x = 7;  
// Your piece of code
var x = "roman" // Here, you override the value of x defined earlier.
alert(x); // "roman"    
But when you use a closure which you have mentioned:    
var x = 7;   
// it doesn't affect/change the value of global x   
(function (){ var x = "roman";})();
alert(x); // 7

在javascript中function（）{}的含义是什么？

3 个答案: