Check an int array for duplicate values. Written for leetcode.com challenge #217.

leetcode-217.js

/**
 * Check an int array for duplicate values.
 * Written for leetcode.com challenge #217.
 *
 * @param {int[]} nums Array of int values to check.
 * @return {boolean} TRUE if duplicate values found, FALSE if every element is distinct.
 *
 * @see https://leetcode.com/problems/contains-duplicate/
 */
var containsDuplicate = function(nums) {
    /**
    * forEach does not allow us to return a value in JavaScript,
    * so the use of a bool value (result) is necessary.
    *
    * @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach
    */
    let result = false;
    let scanned_values = [];
    nums.forEach(
        function(element) {
            if (scanned_values.indexOf(element) == -1) { // indicates no match found
                scanned_values.push(element);
            }
            else { // a match was found
                result = true;
            }
        }
    );
    return result;
};