JavaScript中的默认函数参数

Question

Is it possible to set default parameter values for functions in JavaScript like with PHP?

function phpFunc($param='defvalue'){
    echo $param;
}

phpFunc();

Would result in 'defvalue' being outputted...

Is this possible in javascript?

Thanks.

Answer 1

No, it's not possible. You would have to do something like this :

function jsFunc(param) {
  param = typeof param == 'undefined' ? 'defvalue' : param;
  return param;
}

alert( jsFunc() );               // shows defvalue
alert( jsFunc('Hello, world!');  // shows Hello, world!

Hope this helps!

Answer 2

Or just:

function jsFunc(param){
     param = param || defValue;
     return param;
 }

Answer 3

In Javascript, you can use ES6 Default Value Parameter function to return a default value. So the code should look something like this:

function jsFunc(param='defvalue'){
   return `${param}`;
} 

jsFunc();    // *defvalue*
jsFunc('Welcome');    // *Welcome* 

To create a default parameter, you add an equal sign ( = ) and then whatever you want the parameter to default to if an argument is not provided