How to return part of string before a certain character?

You fiddle already does the job … maybe you try to get the string before the double colon? (you really should edit your question) Then the code would go like this:

str.substring(0, str.indexOf(":"));

Where ‘str’ represents the variable with your string inside.

Click here for JSFiddle Example

Javascript

var input_string = document.getElementById('my-input').innerText;
var output_element = document.getElementById('my-output');

var left_text = input_string.substring(0, input_string.indexOf(":"));

output_element.innerText = left_text;

Html

<p>
  <h5>Input:</h5>
  <strong id="my-input">Left Text:Right Text</strong>
  <h5>Output:</h5>
  <strong id="my-output">XXX</strong>
</p>

CSS

body { font-family: Calibri, sans-serif; color:#555; }
h5 { margin-bottom: 0.8em; }
strong {
  width:90%;
  padding: 0.5em 1em;
  background-color: cyan;
}
#my-output { background-color: gold; }