Scopes

Question 1

What will the below code print out?
"use strict";
var name = 'igloo';
var code = "var name = 'asim';"
eval(code)
console.log(name)

Answer 1

igloo

Question 2

// What will this code print?
    (function(){
      var a = 3;
    })();
    console.log("a defined? " + (typeof a !== 'undefined'));

Answer 2

a defined false

Question 3

// What will this code print?
    console.log(moo);
    var moo = function() {
        console.log("loo");
    };

Answer 3

undefined

Question 4

for (var i = 0; i < 5; i++) {
  var btn = document.createElement('button');
  btn.appendChild(document.createTextNode('Button ' + i));
  btn.addEventListener('click', function(){ console.log(i); });
  document.body.appendChild(btn);
}
// What gets logged to the console when the user clicks on “Button 4”?

Answer 4

5

Question 5

console.log((function f(n){return ((n > 1) ? n * f(n-1) : n)})(4));

Answer 5

This is an IIFE that actually performs a factorial, so 4! which is 24

Question 6

// Consider the code snippet below. What will the console output be?
(function(x) {
    return (function(y) {
        console.log(x);
    })(2)
})(1);

Answer 6

Javascript searches the functions outer scope and in there it will find x and the value of x is 1 since that is what was passed in through the IIFE.

Question 7

// Consider the code snippet below. What will the console output?
function loo() {
  var goo = 1;
  moo();
}
function moo() {
  console.log(goo);
}
loo();

Answer 7

The goo variable isn’t visible on the moo function due to scope lookup rules.

uncaught REferenceError: goo not defined

Question 8

// What will be the output of first console.log in the code below?
var salary = “1000$”;
(function () {
console.log(“Original salary was “ + salary);
var salary = “5000$”;
console.log(“My New Salary “ + salary);
})();

Answer 8

The var salary in the IIFE is hoisted to the top of the function scope, so that means that salary is set to undefined by the time the first console.log is run

Original Salary was undeffined

Question 9

// What happens when you execute the code below
    a = 1;

Answer 9

It creates a global variable called “a”

Question 10

// What does this print out?
    console.log(typeof(null));

Answer 10

Object

Question 11

Can closures refer to variables inside functions (outer scopes)

Answer 11

yes

Question 12

Can closures refer to variables even after the function has been returned?

Answer 12

Yes (only current value of variables)

Question 13

//What does this return 
var foo = [];

for(var i =0; i < 10; i++){
    foo[i] = function() {return i};
}

console. log(foo0);
console. log(foo1);
console. log(foo2);

Answer 13

10
10
10

Why? Because the closure points to the actual value of i in the outer scope (after the for loop has finished)

Question 14

//How to get 1 -3 output from this
var foo = [];
for(var i =0; i < 10; i++){
    foo[i] = function() {return i};
}

console. log(foo0);
console. log(foo1);
console. log(foo2);

Answer 14

var foo = [];
for(var i =0; i < 10; i++){
 // use a intimidate invoked function //
    (function(){
        var y = i;
        foo[i] = function() {return y};
    })();        
}
console.log(foo[0]());
console.log(foo[1]());
console.log(foo[2]());

Question 15

// improve //
var foo = [];
for(var i =0; i < 10; i++){
 // use a intimidate invoked function //
    (function(){
        var y = i;
        foo[i] = function() {return y};
    })();        
}

Answer 15

var foo = [];
for(var i =0; i < 10; i++){
    (function(y){
        foo[y] = function() {return y};
    })(i);     
}