[英]What is the meaning of using done as a parameter in a javascript function?
[英]What is the meaning of function(){} in javascript?
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;
您发布的代码声明了一个名为noop(无操作)的空函数,作为在某些情况下执行的替代方法。 例如代码:
options.ondragover = options.ondragover || noop;
检查options.ondragover
存在,如果不存在,则将空函数分配给该变量。
它只是一个自我执行的函数,您可以在其中声明的任何内容执行相同的函数。
它限制范围并使其私有,并从全局对象中隐藏变量。
// 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
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.