URL query algorithm. A very basic solution to add or replace a property and its value to a URL.

replaceOrAddValue.js

  /*
   * A very basic solution to add or replace a property and its value to a URL
   *
   * Usage example:
   * url = replaceOrAddValue(url, "property_name", "value");
   *
   * Source: https://gist.github.com/kevinweber/58a1b1bdcbab109018dc01a619f9b730
   */
  function replaceOrAddValue(query, variable, value) {
    var findVariable = variable + "=",
      variableIndex = query.indexOf(findVariable),
      hashIndex = query.indexOf('#'),
      hash = '',
      splitQuery,
      queryFirstPart,
      queryLastPart;

    // Extract hash
    if (hashIndex > -1) {
      splitQuery = query.split('#', 2);
      query = splitQuery[0];
      hash = '#' + splitQuery[1];
    }

    // Check if value exists already. "-1" means it doesn't exist yet.
    if (variableIndex === -1) {
      query += query.indexOf('?') === -1 ? '?' : '&';
      query += findVariable + value;
    } else {
      // Split query
      queryFirstPart = query.substring(0, variableIndex);
      queryLastPart = query.substring(variableIndex);

      // Replace value of property
      queryLastPart = queryLastPart.replace(/=[\w-]+/, '=' + value);

      // Stick two parts back together
      query = queryFirstPart + queryLastPart;
    }

    // Add back the hash if there has been one
    query += hash;

    return query;
  }