How I would do this:

// function you can use:
function getSecondPart(str) {
    return str.split('-')[1];
}
// use the function:
alert(getSecondPart("sometext-20202"));

Assuming that your string is formatted with newlines between each question and answer pair:

1. Split the entire string by each newline:

var questionAnswerStringPairs = string.split('\n');

This will create an array of questions and answer strings. Each answer will be separated by an '*'.

2. Map over the resulting array, and create matching objects:

// This will store our data.
var questionAnswerPairs = {};

// Let's go through each string from step one and add the question and
// its answer to our object.
questionAnswerStringPairs.forEach( function(pair) {
  // split the string at the *
  pair = pair.split('*');

  // pair is now an array, the first element is the question string
  // the second element is the answer. Let's set those!
  var question = pair[0];
  var answer = pair[1];

  // now let's store that info in the object.
  questionAnswerPairs[question] = answer;
});

Now, you can do this: questionAnswerPairs['question i want the answer to'], or this: questionAnswerPairs[stringObjectWithQuestion] and you will get back your answer!

You can use String.slice with String.lastIndexOf:

var str = 'test/category/1';
str.slice(0, str.lastIndexOf('/') + 1);
// => "test/category/"
str.slice(str.lastIndexOf('/') + 1);
// => 1

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; }