Confusing ScriptObjectMirror size() vs mirror.get("length")

[Art Fiedler]

@Sundararajan

When looping an array in javascript I would typically do something like
this...

    for(var i = 0; i < arr.length; i++) {
        console.log('Index: ' + i + ' = ' + arr[i]);
    }

When looping a javascript array using the ScriptObjectMirror I would
initially think to use the same syntax, however I would swap .length with
.size() since that method is available.

.size() however is not the same as .length in this case. I'm not saying
that is a bug, just noting the confusion it could cause when/if someone
write's a java loop like that and in the future they run into an undefined
item in the middle of the javascript array. See this example...

Thanks,
Arthur Fiedler

    public static void main(String[] args) throws Exception {
        NashornScriptEngineFactory factory = new
NashornScriptEngineFactory();
        ScriptEngine scriptEngine = factory.getScriptEngine();
        scriptEngine.eval(
                "globalArray = new Array(3);\n" +
                "globalArray[0] = 'line1';\n"+
                "globalArray[2] = 'line3';\n"); // Note index 1 was skipped
        ScriptObjectMirror array =
(ScriptObjectMirror)scriptEngine.get("globalArray");
        System.out.println("entrySet.size(): " + array.entrySet().size());
        System.out.println("keySet.size(): " + array.keySet().size());
        System.out.println("values.size(): " + array.values().size());
        System.out.println("length: " + array.get("length"));
        System.out.println("size(): " + array.size());
        for(int i = 0; i < array.size(); i++) {
            System.out.println("Index: " + i);
            String iStr = String.valueOf(i);
            System.out.println("    Get('"+iStr+"'): " + array.get(iStr));
        }
        System.out.println("what happened to index 2?? oops!");
    }
    /*
    entrySet.size(): 2
    keySet.size(): 2
    values.size(): 2
    length: 3
    size(): 2
    Index: 0
        Get('0'): line1
    Index: 1
        Get('1'): null
    what happened to index 2?? oops!
    */