JavaScript MCQ: JavaScript Multiple Choice Questions and Answers

How does the forEach() method differ from a for statement?

What would be the result in the console of running this code?
for (var i = 0; i < 5; i++) {
console.log(i);
}

Which property references the DOM object that dispatched an event?

This program has a problem. What is it?

var a;
var b = (a = 3) ? true : false;

Which statement sets the Person constructor as the parent of the Student constructor in the prototype chain?

Which choice is not a unary operator?

. Which Object method returns an iterable that can be used to iterate over the properties of an object?

Which statement selects all img elements in the DOM tree?

Which method converts JSON data to a JavaScript object?

Which class-based lifecycle method would be called at the same time as this effect Hook?

useEffect(() => {
// do things
}, []);

What type of scope does the end variable have in the code shown?
var start = 1;
if (start === 1) {
let end = 2;
}

What's one difference between the async and defer attributes of the HTML script tag?

What value does this code return?
let answer = true;
if (answer === false) {
return 0;
} else {
return 10;
}

Which expression evaluates to true?

How is a forEach statement different from a for statement?

What is the result in the console of running the code shown?
var Storm = function () {};
Storm.prototype.precip = 'rain';
var WinterStorm = function () {};
WinterStorm.prototype = new Storm();
WinterStorm.prototype.precip = 'snow';
var bob = new WinterStorm();
console.log(bob.precip);

When would 'results shown' be logged to the console?

let modal = document.querySelector('#results');
setTimeout(function () {
modal.classList.remove('hidden');
}, 10000);

Why might you choose to make your code asynchronous?

What two values will this code print?
function printA() {
console.log(answer);
var answer = 1;
}
printA();
printA();

Review the code below. Which statement calls the addTax function and passes 50 as an argument?
function addTax(total) {
return total * 1.05;
}

What is the output of this code?
var obj;
console.log(obj);

Which choice is valid example for an arrow function?

Which statement references the DOM node created by the code shown?
<p class="pull">lorem ipsum</p>

Which of these is a valid variable name?

Which event is fired on a text field within a form when a user tabs to it, or clicks or touches it?

What is one difference between collections created with Map and collections created with Object?

What is the name of a function whose execution can be suspended and resumed at a later point?

What is the result in the console of running this code?
'use strict';
function logThis() {
this.desc = 'logger';
console.log(this);
}
new logThis();

For the following class, how do you get the value of 42 from an instance of X?
class X {
get Y() {
return 42;
}
}

What is the result in the console of running this code?
function logThis() {
console.log(this);
}
logThis();

Which of the following operators can be used to do a short-circuit evaluation?

. You've written the event listener shown below for a form button, but each time you click the button, the page reloads. Which statement would stop this from happening?
button.addEventListener(
'click',
function (e) {
button.className = 'clicked';
},
false,
);

When would the final statement in the code shown be logged to the console?
let modal = document.querySelector('#result');
setTimeout(function(){
modal.classList.remove('hidden);
}, 10000);
console.log('Results shown');

Which statement is the correct way to create a variable called rate and assign it the value 100?

Which keyword is used to create an error?

What is the result in the console of running the code shown?
var start = 1;
function setEnd() {
var end = 10;
}
setEnd();
console.log(end);

Which method cancels event default behavior?

. What is the value of dessert.type after executing this code?
const dessert = { type: 'pie' };
dessert.type = 'pudding';

You need to match a time value such as 12:00:32. Which of the following regular expressions would work for your code?

Which statement creates a new object using the Person constructor?

You're adding error handling to the code shown. Which code would you include within the if statement to specify an error message?
function addNumbers(x, y) {
if (isNaN(x) || isNaN(y)) {
}
}

. How many prototype objects are in the chain for the following array?
let arr = [];

Which method do you use to attach one DOM node to another?

Why would you choose an asynchronous structure for your code?

What does the following expression evaluate to?

[] == [];

Which of the following is not a keyword in JavaScript?

How does a function create a closure?

How would you reference the text 'avenue' in the code shown?
let roadTypes = ['street', 'road', 'avenue', 'circle'];

Which method is called automatically when an object is initialized?

What will this code log in the console?
function sayHello() {
console.log('hello');
}

console.log(sayHello.prototype);

Which statement is true about Functional Programming?

What will the value of y be in this code:
const x = 6 % 2;
const y = x ? 'One' : 'Two';

. How would you use the TaxCalculator to determine the amount of tax on $50?
class TaxCalculator {
static calculate(total) {
return total * 0.05;
}
}

Which statement represents the starting code converted to an IIFE?

What will this code print?
var v = 1;
var f1 = function () {
console.log(v);
};

var f2 = function () {
var v = 2;
f1();
};

f2();

What is the HTTP verb to request the contents of an existing resource?

Which collection object allows unique value to be inserted only once?

Why is it usually better to work with Objects instead of Arrays to store a collection of records?

When would you use a conditional statement?

Which choice is an incorrect way to define an arrow function that returns an empty object?

Which of the following values is not a Boolean false?

What will be logged to the console?
'use strict';
function logThis() {
this.desc = 'logger';
console.log(this);
}
new logThis();

What is the result of running this code?
sum(10, 20);
diff(10, 20);
function sum(x, y) {
return x + y;
}

let diff = function (x, y) {
return x - y;
};

Which statement is true about the "async" attribute for the HTML script tag?

Which Variable-defining keyword allows its variable to be accessed (as undefined) before the line that defines it?

Which statement creates a new function called discountPrice?

Why would you include a "use strict" statement in a JavaScript file?

How do you import the lodash library making it top-level Api available as the "_" variable?

After the following code, what is the value of a.length?
var a = ['dog', 'cat', 'hen'];
a[100] = 'fox';
console.log(a.length);

Which variable is an implicit parameter for every function in JavaScript?

What is the result of running this statement?
console.log(typeof(42));

0 && hi

Which statement is used to skip iteration of the loop?

What will be logged to the console?
var a = ['dog', 'cat', 'hen'];
a[100] = 'fox';
console.log(a.length);

For the following class, how do you get the value of 42 from "X" ?
class X {
get Y() {
return 42;
}
}
var x = new X();

Your code is producing the error: TypeError: Cannot read property 'reduce' of undefined. What does that mean?

If you attempt to call a value as a function but the value is not a function, what kind of error would you get?

Which operator returns true if the two compared values are not equal?

What is the result of running the statement shown?
let a = 5;
console.log(++a);

You've written the code shown to log a set of consecutive values, but it instead results in the value 5, 5, 5, and 5 being logged to the console. Which revised version of the code would result in the value 1, 2, 3 and 4 being logged?
for (var i = 1; i <= 4; i++) {
setTimeout(function () {
console.log(i);
}, i * 10000);
}

Which concept is defined as a template that can be used to generate different objects that share some shape and/or behavior?

How do you add a comment to JavaScript code?