javascript - 如何在Javascript中声明可选的函数参数？ [重复](How can I declare optional function parameters in Javascript? [duplicate])

Question

Possible Duplicate:

(可能重复：)

Is there a better way to do optional function parameters in Javascript?

(有没有更好的方法在Javascript中执行可选的函数参数？)

Can I declare default parameter like

(我可以声明默认参数吗？)

function myFunc( a, b=0) 
{ 
  // b is my optional parameter 
} 

in javascript.

(在javascript中。)

  ask by Uttam Dutta translate from so

Answer 1

With ES6: This is now part of the language :

(使用ES6：现在这是语言的一部分 ：)

function myFunc(a, b = 0) {
   // function body
}

Please keep in mind that ES6 checks the values against undefined and not against truthy-ness (so only real undefined values get the default value - falsy values like null will not default).

(请记住，ES6检查undefined的值而不是truthy-ness（因此只有真正的未定义值才能获得默认值 - 像null这样的假值不会默认值）。)

---

With ES5:

(使用ES5：)

function myFunc(a,b) {
  b = b || 0;

  // b will be set either to b or to 0.
}

This works as long as all values you explicitly pass in are truthy .

(只要您明确传入的所有值都是真实的，这就可以正常工作 。)

Values that are not truthy as per MiniGod's comment: null, undefined, 0, false, ''

(根据MiniGod的评论不是真正的值： null, undefined, 0, false, '')

It's pretty common to see JavaScript libraries to do a bunch of checks on optional inputs before the function actually starts.

(在函数实际启动之前，看到JavaScript库对可选输入进行一系列检查是很常见的。)