Compare part of string in JavaScript

Question

How do I compare a part of a string - for example if I want to compare if string A is part of string B. I would like to find out this: When string A = \"abcd\"

Answer 1

Using indexOf or match is unnecessarily slow if you are dealing with large strings and you only need to validate the beginning of the string. A better solution is to use startsWith() or its equivalent function-- from https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/startsWith:

if (!String.prototype.startsWith) {
    String.prototype.startsWith = function(searchString, position){
      position = position || 0;
      return this.substr(position, searchString.length) === searchString;
  };
}