[Javascript] How do you return more than one values from a function ?

[Paul Novitski]

At 04:31 PM 7/2/2004, dev at qroute.net wrote:
>Is byref allowed in JS ?
>
>function isValidEmail(emailStr, byref reason)
>{
>     reason='abc'
>     return false
>     // is something like this possible
>}


Not the way you've shown, but your goal of modifying multiple variables 
with a single function call is possible using other methods.

All arguments to JavaScript functions are passed by value; if a function 
attempts to modify an argument, the variable passed by the calling script 
is unchanged:

         function CallingFunction()
         {
                 var i = 5;
                 DoIt(i);
                 alert("i = " + i);
         }

         function DoIt(argI)
         {
                 argI = 10;
         }

Result:  i = 5 (unchanged)

However, here are three ways you can get a function to modify multiple 
values, perceivable by the calling script:


1) Declare global variables and pass them to a function that receives the 
values but modifies the global variables:

         // we're not inside a function, so these variables are global:
         var globalI = 5;
         var globalJ = 7;

         ModifyGlobals(globalI, globalJ);

         alert("globalI = " + globalI);
         alert("globalJ = " + globalJ);

         function ModifyGlobals(argI, argJ)
         {
                 globalI = argI * 1234567;
                 globalJ = argJ - 2.3;
         }

This has the appearance of modifying arguments passed by reference but 
really doesn't.


2) Return an array of values.  (I'm using named array members here, but 
numerically indexed elements work the same.)

         function CallingFunction()
         {
                 var a = new Array();
                 a.flies = 3;
                 a.frogs = 5;

                 a = ChangeValues(a);

                 alert("flies = " + a.flies);
                 alert("frogs = " + a.frogs);
         }

         function ChangeValues(argArray)
         {
                 argArray.flies = 23;
                 argArray.frogs = 11;
                 return argArray;
         }


3) Similar to example 2 but using object constructor syntax, so that the 
properties of the new object are globally visible:

         function CallingFunction()
         {
                 var oResult = new Venusian(3, 7);

                 alert("eyes = " + oResult.eyes);
                 alert("tentacles = " + oResult.tentacles);
         }

         function Venusian(argEyes, argTentacles)
         {
                 this.eyes = argEyes * 3;
                 this.tentacles = argTentacles * 7;
         }

Since a JavaScript array really is an object and can have named properties 
(elements), there's probably no need to go beyond example 2) unless you do 
need a new object with custom functions built in.

Regards,
Paul