Skype Technical Interview's Questions about JavaScript

skype-interview.js

/**
 * Write a JavaScript function that takes a number n and returns the sum of the even numbers from 1 to n.
 */
function firstFunc(n) {
    let result = 0;
    for (let index = 1; index <= n; index++) {
        if (index % 2 === 0) {
            result += index;
        }
    }
    return result;
}

/**
 * Write a function that takes an integer n and returns the next number greater than n that is a multiple of 7.
 */
function secondFunc(n) {
    if (n < 7) { return 7; }
    for (var aux = 1; aux * 7 <= n; aux++) {}
    return aux * 7;
}

/**
 * Write the "Factorial" function recursively, without using a loop: "function factorial ( n ) {…}"
 * (A factorial is the product of a positive number and all the numbers below it.
 * So the factorial of 4 equals 4 x 3 x 2 x 1 = 24. The factorial of 1 equals 1.)
 */
function factorial(n) {
    return n > 1 ? n * factorial(n - 1) : 1;
}

/**
 * What would this function return?
 * 
 * Returns `undefined`.
 */
function foo() {
    return
    {
        bar: "hello"
    };
}

/**
 * What is a "closure" in JavaScript?
 * 
 * Closures are functions that refer to independent (free) variables (variables that are used locally,
 * but defined in an enclosing scope). In other words, these functions 'remember' the environment in which they were created.
 */
(function init(name) {
    (function displayName() {
        alert(name);
    })();    
})('Flavio');

/**
 * How does the "this" keyword work in JavaScript?
 * 
 * See this link http://javascriptissexy.com/understand-javascripts-this-with-clarity-and-master-it/ for a full-detail explanation.
 */

/**
 * What do the "apply" and "call" functions do? What are the differences between the two?
 * 
 * The `apply()` method calls a function with a given `this` value and arguments provided as an array (or an array-like object).
 * The `call()` method calls a function with a given `this` value and arguments provided individually.
 * While the syntax of this function is almost identical to that of `call()`,
 * the fundamental difference is that `call()` accepts an argument list, while `apply()` accepts a single array of arguments.
 */
function log(x, y, z) {
    console.log(x, y, z);
}
var args = [1, 2, 3];
log.apply(null, args);      // with `apply()`
log.call(null, ...args);    // with `call()`