javascript作用_防止JavaScript产生副作用

Myth丶恋晨 2023-02-22 03:41 83阅读 0赞

javascript作用

JavaScript is very dynamic these days but I still see a lot of legacy code, whether it be for optimal backward compatibility or simply that the code hasn't been maintained.  One of the practices that makes me cringe is coding that creates unwanted side effects.  What's a side effect?  A piece of code whereby a variable is created and available throughout a scope when it doesn't need to be.  Let me show you a few examples and how to avoid these unwanted side effects.

如今，JavaScript是非常动态的，但我仍然看到很多旧代码，无论是为了实现最佳的向后兼容性，还是仅仅是未维护代码。 使我畏缩的一种做法是编码，该编码会产生有害的副作用。 有什么副作用？ 一段代码，通过该代码可以创建变量，并在不需要时将其在整个作用域中使用。 让我向您展示一些示例，以及如何避免这些不良副作用。

## `Array.prototype.forEach()`代替`for(var x = ...)` **(**`Array.prototype.forEach()` instead of `for(var x = ...)`**)** ##

Looping through a JavaScript array was traditionally done via a `for()` loop:

传统上，通过`for()`循环在JavaScript数组中循环：

var myArray = [1, 2, 3];
    
    for(var x=0, length = myArray.length; x < length; x++) {
    	// ...
    }
    
    // "x" and "length" are side effects

The side effect of this pattern is at minimum the running index, if not the length as well -- they are available within the entire scope.  `Array` prototype methods like `map`, `forEach`, and `every` allow the developer to avoid these side effects:

这种模式的副作用至少是运行索引，即使不是长度也是如此-它们在整个范围内都可用。 `Array`原型方法，例如`map` ， `forEach`和`every`方法，使开发人员可以避免以下副作用：

[1, 2, 3].forEach(function(item, index, array) {
    	// No side effects! :)
    });

No "utility" variables need to be created for the looping, thus avoiding side effects. This is called "functional" programming.

无需为循环创建“实用程序”变量，从而避免了副作用。 这称为“功能”编程。

## 自执行功能 **(**Self-Executing Functions**)** ##

If you haven't read [Hiding Your Privates with JavaScript][], and you don't know how to keep private variables in JavaScript, take a few minutes to read it.  The same pattern provided in that post allows you to avoid side effects via self-executing functions:

如果您还没有阅读[使用JavaScript隐藏私人信息][Hiding Your Privates with JavaScript] ，并且不知道如何在JavaScript中保留私人变量，请花几分钟的时间阅读它。 该帖子中提供的相同模式允许您通过自执行函数避免副作用：

// Example from MooTools source...
    
    Browser.Request = (function(){
    
    	var XMLHTTP = function(){
    		return new XMLHttpRequest();
    	};
    
    	var MSXML2 = function(){
    		return new ActiveXObject('MSXML2.XMLHTTP');
    	};
    
    	var MSXML = function(){
    		return new ActiveXObject('Microsoft.XMLHTTP');
    	};
    
    	return Function.attempt(function(){
    		XMLHTTP();
    		return XMLHTTP;
    	}, function(){
    		MSXML2();
    		return MSXML2;
    	}, function(){
    		MSXML();
    		return MSXML;
    	});
    
    })();
    
    // The three vars are stuck in the self-executing function, they don't "leak" out

The gist is that you can do loads of processing within the self-executing function (a new scope) without allowing variables leaking out -- the only item returned or leaked is the desired return value.

要点是，您可以在自执行函数(新作用域)中执行大量处理，而不会让变量泄漏出去-返回或泄漏的唯一项是所需的返回值。

Tightening up your code includes avoiding side effects and JavaScript makes it easy if you follow these basic practices!

加强代码包括避免副作用，如果您遵循这些基本做法，JavaScript会很容易！

> 翻译自: [https://davidwalsh.name/preventing-sideeffects-javascript][https_davidwalsh.name_preventing-sideeffects-javascript]

javascript作用

[Hiding Your Privates with JavaScript]: https://davidwalsh.name/javascript-private
[https_davidwalsh.name_preventing-sideeffects-javascript]: https://davidwalsh.name/preventing-sideeffects-javascript