You have entered 5 instead of 0 here:
var trimmedString = string.substring(5, length); //should be 0
Doing this will only show the first 5 characters:
var length = 5; //number of characters
Assuming that dataset1 is the name of the dataset connected to your repeater, have you done this?
Resources for JS:
JavaScript | MDN
https://www.javascript.com/
JavaScript Tutorial
JavaScript Tutorial - Learn JavaScript
