demo/typescript.js
function forEach(array, callback) {
        if (array) {
            for (var i = 0, len = array.length; i < len; i++) {
                var result = callback(array[i], i);
                if (result) {
                    return result;
                }
            }
        }
        return undefined;
    }
function forEach(array, callback) {
        if (array) {
            for (var i = 0, len = array.length; i < len; i++) {
                var result = callback(array[i], i);
                if (result) {
                    return result;
                }
            }
        }
        return undefined;
    }
Iterates through 'array' by index and performs the callback on each element of array until the callback
returns a truthy value, then returns that value.
If no such value is found, the callback is applied to each element of array and undefined is returned.