Wednesday, February 4, 2009

ExternalInterface vs. JS function returning empty-string

The Problem

I have a JavaScript function that always returns a string, but in some cases it needs to return an empty-string. I have Flash, using ActionScript 2, call this function using, but surprisingly when the return value of the JavaScript function is empty-string, returns the 4-character string: "null". If using ActionScript 3, the value null is returned instead of the string.

function test(bln)
   return (bln ? "some text" : "");

import flash.external.*;
    "'" +"test", true) + "'");
    //alerts: 'some text'
    "'" +"test", false) + "'");
    //alerts: 'null'

The Solution

The workaround is to detect "null" or null and replace it with empty-string, as in these examples:

ActionScript 2 workaround
import flash.external.*;

var x ="test", false);

if (x == "null")
    x = "";"alert", "'" + x + "'"); //alerts: ''

ActionScript 3 workaround
import flash.external.*;

var x ="test", false);

if (x == null)
    x = "";"alert", "'" + x + "'"); //alerts: ''

1 comment:

  1. I've just discovered this in AS2. My return value is a structured object but every element that holds an empty string, comes back as the 4-character string 'null'. This must be a bug surely! Having to parse my returned object converting 'null' (string) back to '' (string) is going to be a pain.

    It would be nice to know why the interface's data is marshalled this way.


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