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; }

Another method could be to split the string by ":" and then pop off the end. var newString = string.split(":").pop();