JavaScript中的return语句错误

Question

I have this javascript code which is not working.

function myfun()
   {
       return
       {
       alert("para"); 
       } 
   };

   myfun();

I have read about the javascript's automatic semicolon insertion. I corrected the above code as

return{
       alert("para"); 
       } 

But still got the error : unexpected token ( . I wonder why?

NOTE: I don't need the solution but I need the explanation why the above code in not working.

EDIT

According to the book, javascript the good parts, the return statement if returns value must be in same line as return expression.

ie

 return {
status: true
};

AND

 return
{
status: true
};

Is wrong.Then How come

function myfun(para)
   {
     var status; 

       return
       {
          status : alert(para)
       };
   };


  myfun("ok");

produce no error.It won't work but shows no error as well.It works when the { is in the same line as return.

ie

 function myfun(para)
   {
     var status; 

       return{
          status : alert(para)
       };
   };

   myfun("ok");

Answer 1

In

return {
   alert("para"); 
} 

the {...} are interpreted as object literal . An object literal has the form

{
    key: value,
    //...
}

Object literals cannot contain arbitrary statements.

Answer 2

Looks like you've difficulties with ASI and the difference between run-time and parsing-time.

Where as

return {
    status: true
};

is a correct way to return an object, ASI will take an action in the following code:

return
{ //  ^-- ASI will insert a semicolon here
    status: true
};

The semicolon is automatically inserted, and at run-time all lines after return are ignored. However, at parsing time , everything counts, and if there's a syntax error, like in your first example, an error will be thrown.

Answer 3

The reason why you are getting that error is because JS is expecting a value to the key "para".

There is no compulsion to return in a JavaScript function. If your intention is to test if the control goes to the function, you can simply change it to

function myfun() { alert("para"); }

if you want to return an object with string "para" you should change it to

function myfun() { return { "text": "para" }; }