javascript - Default Parameters in Function Expressions

Question

Default parameters in javscript function declerations can be achieved with a simple assignment as follows:

function foo(arg1 = 'default1', arg2 = 'default2') { ... }

But how can I have default parameters for function expressions, as the following does NOT work in chrome v47:

var foo = function (arg1 = 'default1', arg2 = 'default2') { ... }

Any pointers would be helpful.

Answer 1

これを JavaScript で行うことはできません。

function foo(arg1 = 'default1', arg2 = 'default2') { ; }

コンソールで確認すると、構文エラーが発生します。あなたはこれを行うことができます：

function foo(arg1, arg2) {
   if ("undefined" == typeof arg2) {
       arg2 = "default2";
   }
}

var foo2 = function(arg1, arg2) {
   if ("undefined" == typeof arg2) {
       arg2 = "default2";
   }
}