JavaScript syntax basics: run-through¶

For your convenience, we have collected the basics of JavaScript in a cheatsheet.

Below, some questions to check that the JavaScript syntax is read and understood.

Question 1

How is an external JavaScript loaded into a document

Question 2

Where in a document can you include JavaScript?

Inside the head element

Inside the body element

Inside either head or body element

Question 4

How do you specify a block-scope constant tmp with value 2 that will not be changed?

int tmp = 2;

const tmp = 2;

tmp = 2;

let tmp =2;

var tmp = 2;

Question 5

What is a block?

code rows that get auto-indented similarly

statements grouped by some entity, e.g., function

something within curly brackets

the inner content of a control structure such as for or while

Question 6

What is the term for raising var declarations to have a function-scope visibility even if the var variables were defined inside an inner-block of a function?

Question 7

Which of the following code snippets are correct and not causing any errors?

// a
function sayHi() {console.log('hi!')}
sayHi()

// b
sayHi()
function sayHi() {console.log('hi!')}

// c
var sayHi = function sayHi() {console.log('hi!')}
sayHi()

// d
sayHi()
var sayHi = function sayHi() {console.log('hi!')}

// e
(function sayHi() {
  console.log('hi!')
})()

a is OK

b is OK

c is OK

d is OK

e is OK

Question 8

(function sayHi() {
  console.log('hi!')
})()

() in the end of the function above implies that ..

e is a function

e does not take any parameters

e is self-invoked

Question 9

Data types can be primitives or objects

primitives have to be instantiated with a keyword new

built-in objects are often instantiated with a keyword new

everything instantiated with new has to be deleted expliticly

primitives include int, float, string, and object

Question 10

== comparison

causes type coercions

prints false when console.log(1 == ‘1’) is called

is called a strict comparison

Question 11

=== comparison

causes type coercions

prints false when console.log(1 === ‘1’) is called

is called a strict comparison

Question 12

How can you specify an array with initial values in JavaScript?

let arr = [1, 2, 3];

let arr = {1, 2, 3};

const arr = (1, 2, 3);

Question 13

Define an empty array with two characters only (i.e., the max-length of the definition is two chars):

let array1 =  ...

Question 14

Define an empty object (used as an associative array or map) with two characters only:

let object1 = ...

Question 15

Functions in JavaScript

are first-class citizens

print object if typeof() is called having a function as an argument

are objects

can be assigned to a variable

Question 16

If a following JavaScript Snippet is executed, what will happen?

function examineArguments(a,b,c){
    console.log(a,b,c);
}
const a=1; const b=2; const c=3;
const d=4; const e=5; const f=6;
examineArguments(a,b,c,d,e,f);

a runtime error will be thrown

the program will print “1 2 3”

function cannot be found since the signature differs from what is expected

Question 17

Following JavaScript Snippet is executed, what will happen:

function examineArguments(a, b ,c){
    console.log(a, b, c);
}
const a = 1; const b = 2; const c = 3;
examineArguments(a, b);

a runtime error will be thrown

the program will print “1 2”

the program will print “1 2 3”

the program will print “1 2 undefined”

Question 18

Which of the following does specify a function that will return a number?

function myFunction() { return 3; }

public Number function myFunction() { return 3; }

var myFunction = function() { return 3; }

Number function myFunction() { return 3; }

Question 19

function addTenStupid(num) {
  for(i=0; i < 10; i++) { num += 1; }
  return num;
}

function addThousandStupid(num) {
  for(i=0; i < 100; i++) { num += addTenStupid(0); }
  return num;
}
console.log(addTenStupid(0));
console.log(addTenStupid(5));
console.log(addThousandStupid(1));

addTenStupid(0), first console log, prints 10

addTenStupid(5), second console log, prints 15

addThousandStupid(1) prints nothing

this example is to demonstrate that global variables are evil