Multiple selections from drop down list or list box to text field

Hi gurus,

I came across the situation where I want to select multiple value from list box and display those selected values to Text field.

For eg: Lets say we have 2 fields. one is  list box. another is Text field. My  List box contains 

Red

Blue

Green

Yellow

Black

If user selects Red, Blue and Yellow. Then I want to display these 3 values on the Text field simultaneously.

Now, I have seen the code where  var v = this.getField("ListBox1"); but the issue is I dont have this functionality(this.getField) in my adobe livecycle designer.Attached ss of not having functionality. so can you pls provide js or any solution through which I can resolve this.