有没有更好的方法在JavaScript中执行可选的函数参数？ [重复]

本文翻译自：Is there a better way to do optional function parameters in JavaScript? [duplicate]

This question already has an answer here:这个问题在这里已有答案：

Set a default parameter value for a JavaScript function 24 answers为JavaScript函数设置 24个答案 的默认参数值

I've always handled optional parameters in JavaScript like this:我总是在JavaScript中处理可选参数，如下所示：

function myFunc(requiredArg, optionalArg){optionalArg = optionalArg || 'defaultValue';// Do stuff}

Is there a better way to do it?有没有更好的方法呢？

Are there any cases where using||有没有使用||like that is going to fail?那会失败吗？

#1楼

参考：/question/cjd/有没有更好的方法在JavaScript中执行可选的函数参数-重复

#2楼

If you're using defaults extensively, this seems much more readable:如果你广泛使用默认值，这似乎更具可读性：

function usageExemple(a,b,c,d){//defaultsa=defaultValue(a,1);b=defaultValue(b,2);c=defaultValue(c,4);d=defaultValue(d,8);var x = a+b+c+d;return x;}

Just declare this function on the global escope.只需在全局escope上声明此函数即可。

function defaultValue(variable,defaultValue){return(typeof variable!=='undefined')?(variable):(defaultValue);}

Usage patternfruit = defaultValue(fruit,'Apple');用法模式fruit = defaultValue(fruit,'Apple');

*PS you can rename thedefaultValuefunction to a short name, just don't usedefaultit's a reserved word in javascript.* PS你可以将defaultValue函数重命名为一个简短的名称，只是不要使用default它是javascript中的保留字。

#3楼

Your logic fails if optionalArg is passed, but evaluates as false - try this as an alternative如果传递了OptionalArg，您的逻辑将失败，但计算结果为false - 请尝试将此作为替代方法

if (typeof optionalArg === 'undefined') { optionalArg = 'default'; }

Or an alternative idiom:或另类成语：

optionalArg = (typeof optionalArg === 'undefined') ? 'default' : optionalArg;

Use whichever idiom communicates the intent best to you!使用哪个成语最能传达您的意图！

#4楼

You can use some different schemes for that.你可以使用一些不同的方案。I've always tested for arguments.length:我一直在测试arguments.length：

function myFunc(requiredArg, optionalArg){optionalArg = myFunc.arguments.length<2 ? 'defaultValue' : optionalArg;...

-- doing so, it can't possibly fail, but I don't know if your way has any chance of failing, just now I can't think up a scenario, where it actually would fail ...- 这样做，它不可能失败，但我不知道你的方式是否有任何失败的机会，只是现在我想不出一个场景，它实际上会失败...

And then Paul provided one failing scenario !-)然后保罗提供了一个失败的场景！ - ）

#5楼

If you need to chuck a literalNULLin, then you could have some issues.如果你需要在文字中插入NULL，那么你可能会遇到一些问题。Apart from that, no, I think you're probably on the right track.除此之外，不，我认为你可能走在正确的轨道上。

The other method some people choose is taking an assoc array of variables iterating through the argument list.一些人选择的另一种方法是在参数列表中迭代一组关联变量。It looks a bit neater but I imagine it's a little (very little) bit more process/memory intensive.它看起来有点整洁，但我想它有点（很少）更多的进程/内存密集。

function myFunction (argArray) {var defaults = {'arg1' : "value 1",'arg2' : "value 2",'arg3' : "value 3",'arg4' : "value 4"}for(var i in defaults) if(typeof argArray[i] == "undefined") argArray[i] = defaults[i];// ...}

#6楼

In ECMAScript (aka "ES6") you can declare default argument values in the function declaration:在ECMAScript （又名“ES6”）中，您可以在函数声明中声明默认参数值：

function myFunc(requiredArg, optionalArg = 'defaultValue') {// do stuff}

More about them in this article on MDN .关于MDN的这篇文章中有关它们的更多信息。

This is currently only supported by Firefox , but as the standard has been completed, expect support to improve rapidly.目前仅支持Firefox ，但随着标准的完成，预计支持将迅速提升。

EDIT (-06-12):编辑（-06-12）：

Default parameters are now widely supported by modern browsers.现在，浏览器广泛支持默认参数。All versions of Internet Explorer do not support this feature.所有版本的Internet Explorer都不支持此功能。However, Chrome, Firefox, and Edge currently support it.但是，Chrome，Firefox和Edge目前支持它。

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