How can I check if a value already exists in a ListBox in Java Script

Question

The Answer for the code behind was given as follows:

if (!listBoxInstance.Items.Contains("some text")) // case sensitive is not important
            listBoxInstance.Items.Add("some text");
if (!listBoxInstance.Items.Contains("some text".ToLower())) // case sensitive is important  
            listBoxInstance.Items.Add("some text".ToLower());

Now how would this be done in Java Script? TIA.

Answer 1

Is this listBox.items an object? If so:

if (!listBoxInstance.Items["some text"]) // case sensitive is not important
            listBoxInstance.Items["some text"] = // the value of the property you want to assign;
if (!listBoxInstance.Items[`${"some text".toLowerCase()}`]) // case sensitive is important  
            listBoxInstance.Items[`${"some text".toLowerCase()}`);