Fundamentals 2

Question 1

How do you do a String Conversion?

Answer 1

String(value) function to convert a value to a string:
let value = true;
alert(typeof value); // boolean

value = String(value); // now value is a string “true”
alert(typeof value); // string

Question 2

How do you do Numeric Conversions?

Answer 2

Numeric conversion happens in mathematical functions and expressions automatically:
alert( “6” / “2” ); // 3, strings are converted to numbers

We can use the Number(value) function to explicitly convert a value to a number:
let str = "123";
alert(typeof str); // string

let num = Number(str); // becomes a number 123

alert(typeof num); // number

Question 3

What’s an example of when you would need to use explicit Numeric Conversion?

Answer 3

When we read a value from a string-based source like a text form but expect a number to be entered.

If the string is not a valid number, the result of such a conversion is NaN. For instance:

let age = Number("an arbitrary string instead of a number");
alert(age); // NaN, conversion failed

Question 4

What are four Numeric Conversion rules?

Answer 4

Value:	Becomes…
undefined:	NaN
null:	0
true and false:	1 and 0
string:	Whitespaces from the start and end are removed. If the remaining string is empty, the result is 0. Otherwise, the number is “read” from the string. An error gives NaN.

Question 5

What are examples of Boolean Conversions?

Answer 5

alert( Boolean(1) ); // true
alert( Boolean(0) ); // false

alert( Boolean(“hello”) ); // true
alert( Boolean(“”) ); // false

Note:
alert( Boolean(“0”) ); // true, as it is a string that contains something
“0” and space-only strings like “ “ are true as a boolean.

Question 6

What are the four straightforward maths operations?

Answer 6

Addition +
Subtraction -
Multiplication *
Division /

Question 7

How do you use the Remainder operator?

Answer 7

The remainder operator %, despite its appearance, is not related to percents.

The result of a % b is the remainder of the integer division of a by b.

For instance:

alert( 5 % 2 ); // 1, a remainder of 5 divided by 2
alert( 8 % 3 ); // 2, a remainder of 8 divided by 3

Question 8

How do you use the Exponentiation operator?

Answer 8

The exponentiation operator a ** b raises a to the power of b.

In school maths, we write that as ab.

For instance:

alert( 2 ** 2 ); // 2² = 4
alert( 2 ** 3 ); // 2³ = 8
alert( 2 ** 4 ); // 2⁴ = 16
Just like in maths, the exponentiation operator is defined for non-integer numbers as well.

For example, a square root is an exponentiation by ½:

Question 9

What happens when the addition operator is applied only to strings?

Answer 9

it merges (concatenates) them:
let s = "my" + "string";
alert(s); // mystring

Note that if any of the operands is a string, then the other one is converted to a string too!!!

In this context, the + is called the binary plus.

Question 10

What is the unary plus?

Answer 10

It is applied to a single value. It doesn’t do anything to numbers. But if the operand is not a number, the unary plus converts it into a number.

// No effect on numbers
let x = 1;
alert( +x ); // 1

let y = -2;
alert( +y ); // -2

// Converts non-numbers
alert( +true ); // 1
alert( +"" );   // 0
It actually does the same thing as Number(...), but is shorter.

Question 11

What is Operator precedence?

Answer 11

If an expression has more than one operator, the execution order is defined by their precedence, or, in other words, the default priority order of operators.

From school, we all know that the multiplication in the expression 1 + 2 * 2 should be calculated before the addition. That’s exactly the precedence thing. The multiplication is said to have a higher precedence than the addition.

Aka. BODMAS

Question 12

What are these Assignment operators the same as?
Operator then Example
=	x = y
\+=	x += y	
-=	x -= y	
*=	x *= y	
/=	x /= y	
%=	x %= y

Answer 12

=	x = y	x = y
\+=	x += y	x = x + y
-=	x -= y	x = x - y
*=	x *= y	x = x * y
/=	x /= y	x = x / y
%=	x %= y	x = x % y

Question 13

What is Increment?

Answer 13

Increasing a number by one is among the most common numerical operations.

So, there are special operators for it:

Increment ++ increases a variable by 1:

let counter = 2;
counter++;        // works the same as counter = counter + 1, but is shorter
alert( counter ); // 3

Question 14

What is Decrement?

Answer 14

Decreasing a number by one is among the most common numerical operations.

So, there are special operators for it:

Decrement – decreases a variable by 1:

let counter = 2;
counter--;        // works the same as counter = counter - 1, but is shorter
alert( counter ); // 1

Question 15

How does the comma operator work?

Answer 15

The comma operator , is one of the rarest and most unusual operators. Sometimes, it’s used to write shorter code, so we need to know it in order to understand what’s going on.

The comma operator allows us to evaluate several expressions, dividing them with a comma ,. Each of them is evaluated but only the result of the last one is returned.

Here, the first expression 1 + 2 is evaluated and its result is thrown away. Then, 3 + 4 is evaluated and returned as the result.
let a = (1 + 2, 3 + 4);

alert( a ); // 7 (the result of 3 + 4)

Question 16

Why do we need an operator that throws away everything except the last expression (comma operator)?

Answer 16

Sometimes, people use it in more complex constructs to put several actions in one line.

For example:

// three operations in one line
for (a = 1, b = 3, c = a * b; a < 10; a++) {
 ...
}

Such tricks are used in many JavaScript frameworks. That’s why we’re mentioning them. But usually they don’t improve code readability so we should think well before using them.

Question 17

What are comparison operators syntax in js?

Answer 17

==	equal to
===	equal value and equal type
!=	not equal
!==	not equal value or not equal type
>	greater than
<	less than
>=	greater than or equal to	
<=	less than or equal to

Question 18

How do string comparisons work|?

Answer 18

Strings are compared letter-by-letter.

For example:

alert( ‘Z’ > ‘A’ ); // true
alert( ‘Glow’ > ‘Glee’ ); // true
alert( ‘Bee’ > ‘Be’ ); // true

Question 19

How does comparing different types work in javascript?

Answer 19

When comparing values of different types, JavaScript converts the values to numbers.

For example:

alert( ‘2’ > 1 ); // true, string ‘2’ becomes a number 2
alert( ‘01’ == 1 ); // true, string ‘01’ becomes a number 1
For boolean values, true becomes 1 and false becomes 0.

Question 20

A regular equality check == has a problem. It cannot differentiate 0 from false:

alert( 0 == false ); // true
This happens because operands of different types are converted to numbers by the equality operator ==.

What to do if we’d like to differentiate 0 from false?

Answer 20

A strict equality operator === checks the equality without type conversion.

In other words, if a and b are of different types, then a === b immediately returns false without an attempt to convert them.

Let’s try it:

alert( 0 === false ); // false, because the types are different

Question 21

What do comparison operators return?

Answer 21

Comparison operators return a boolean value.

Question 22

What does the if statement do?

Answer 22

The if(…) statement evaluates a condition in parentheses and, if the result is true, executes a block of code.

For example:

let year = prompt(‘In which year was ECMAScript-2015 specification published?’, ‘’);

if (year == 2015) alert( ‘You are right!’ );

Question 23

How do you execute more than one statement within the if statement?

Answer 23

If we want to execute more than one statement, we have to wrap our code block inside curly braces:

if (year == 2015) {
  alert( "That's correct!" );
  alert( "You're so smart!" );
}
We recommend wrapping your code block with curly braces {} every time you use an if statement, even if there is only one statement to execute. Doing so improves readability.

Question 24

Does the if statement convert the expression in its parantheses to boolean?

Answer 24

The if (…) statement evaluates the expression in its parentheses and converts the result to a boolean.

Question 25

What does the else clause do?

Answer 25

The if statement may contain an optional “else” block. It executes when the condition is falsy.

For example:

let year = prompt(‘In which year was the ECMAScript-2015 specification published?’, ‘’);

if (year == 2015) {
  alert( 'You guessed it right!' );
} else {
  alert( 'How can you be so wrong?' ); // any value except 2015
}

Question 26

What does else if do?

Answer 26

Sometimes, we’d like to test several variants of a condition. The else if clause lets us do that.

For example:

let year = prompt(‘In which year was the ECMAScript-2015 specification published?’, ‘’);

if (year < 2015) {
  alert( 'Too early...' );
} else if (year > 2015) {
  alert( 'Too late' );
} else {
  alert( 'Exactly!' );
}

Question 27

What is the conditional operator ‘?’ or ternary operator?

Answer 27

Sometimes, we need to assign a variable depending on a condition.

For instance:

let accessAllowed;
let age = prompt('How old are you?', '');

if (age > 18) {
  accessAllowed = true;
} else {
  accessAllowed = false;
}

alert(accessAllowed);

Question 28

What is the syntax for the ternary operator?

Answer 28

The syntax is:

let result = condition ? value1 : value2;
The condition is evaluated: if it’s truthy then value1 is returned, otherwise – value2.

For example:

let accessAllowed = (age > 18) ? true : false;
Technically, we can omit the parentheses around age > 18. The question mark operator has a low precedence, so it executes after the comparison >.

This example will do the same thing as the previous one:

// the comparison operator "age > 18" executes first anyway
// (no need to wrap it into parentheses)
let accessAllowed = age > 18 ? true : false;
But parentheses make the code more readable, so we recommend using them.

In the example above, you can avoid using the question mark operator because the comparison itself returns true/false:

// the same
let accessAllowed = age > 18;

Question 29

Example of multiple ternary operators vs if statement

Answer 29

let age = prompt(‘age?’, 18);

let message = (age < 3) ? ‘Hi, baby!’ :
(age < 18) ? ‘Hello!’ :
(age < 100) ? ‘Greetings!’ :
‘What an unusual age!’;

alert( message );

if (age < 3) {
  message = 'Hi, baby!';
} else if (age < 18) {
  message = 'Hello!';
} else if (age < 100) {
  message = 'Greetings!';
} else {
  message = 'What an unusual age!';
}

Question 30

Should you use the ternary operator over an if statement in the way an if statement would be used? When should you use one or the other?

Answer 30

It’s not recommended to use the question mark operator in this way.

The notation is shorter than the equivalent if statement, which appeals to some programmers. But it is less readable.

The purpose of the question mark operator ? is to return one value or another depending on its condition. Please use it for exactly that. Use if when you need to execute different branches of code.