Coercion

Question 1

Explicitly coerce the string ‘1’ to a number

Answer 1

let one = Number(‘1’)

Question 2

What is the result of Number(‘cat’)?

Answer 2

NaN

Question 3

What is the result of Number(‘’)?

Answer 3

0

Question 4

What is the result of Number(‘ ‘)?

Answer 4

0

Question 5

What is the result of Number({})?

Answer 5

NaN

Question 6

What is the result of Number([])?

Answer 6

0

Question 7

What is the result of Number([4])?

Answer 7

4

Question 8

What is the result of Number([undefined])?

Answer 8

0

Question 9

What is the result of Number([1,2,3])?

Answer 9

NaN

Question 10

What is the result of Number(undefined)?

Answer 10

NaN

Question 11

What is the result of Number(null)?

Answer 11

0

Question 12

What is the result of Number(true)?

Answer 12

1

Question 13

What is the result of Number(false)?

Answer 13

0

Question 14

How is parseInt different than Number()?

Answer 14

parseInt() can be called on strings containing non-numeric chars after the number to parse.

parseIntalso accepts a second argument called theradix. It specifies the base of the number contained in the string. For example,10101in the binary numbering system (base-2) represents the number 21 in decimal (base-10).

> parseInt(‘10101’, 2)
21

Question 15

What is the result of parseInt(‘12.52’)?

Answer 15

12

Question 16

What is the result of parseInt(‘12oz’)?

Answer 16

12

Question 17

What is the result of parseInt(‘+12oz’)?

Answer 17

12

Question 18

What is the result of Number(‘12oz’)?

Answer 18

NaN

Question 19

Does parseFloat accept a radix argument?

Answer 19

No

Question 20

What is the result of parseFloat(‘12 grams’)?

Answer 20

12

Question 21

What is the result of parseFloat(‘12.2 grams’)?

Answer 21

12.2

Question 22

What is the result of
+”” ?

Answer 22

0

Question 23

What is the result of
+‘1’ ?

Answer 23

1

Question 24

What is the result of
+‘2.3’ ?

Answer 24

2.3

Question 25

What is the result of
+[] ?

Answer 25

0

Question 26

What is the result of
+‘abc’ ?

Answer 26

NaN

Question 27

What data types can you call toString() on?

Answer 27

All data types except null and undefined.

Question 28

how do you call toString() on a number literal?

Answer 28

(23).toString()
or

let number=23;
number.toString()
or

23..toString()

Question 29

What is the result of
true.toString() & false.toString() ?

Answer 29

> true.toString()
‘true’
false.toString()
‘false’

Question 30

What is the result of
> [1, null, 2, undefined, 3].toString()

Answer 30

‘1,,2,,3’
Array.prototype.toStringtreatsnullandundefinedelements as empty values

Question 31

What is the result of
> let obj = {a: ‘foo’, b: ‘bar’}
> obj.toString()

Answer 31

‘[object Object]’

By default,Object.prototype.toStringreturns the string’[object Object]’

Question 32

What is the result of
[1, 2, 3].toString()

Answer 32

‘1,2,3’

Question 33

What is the result of
String(null)

Answer 33

‘null’

Question 34

What is the result of
String(undefined)

Answer 34

‘undefined’

Question 35

What is the result of
toString(null)?

Answer 35

This will throw a TypeError

Question 36

What is the result of
toString(undefined)

Answer 36

This will throw a TypeError

Question 37

What is the result of
String(42)

Answer 37

‘42’

Question 38

What is the result of
‘1’ === 1?

Answer 38

false

Question 39

What is the result of
‘1’ == 1?

Answer 39

true
The non-strict equality operator coerces the string’1’into a number and then compares it with the1on the right-hand side.

Question 40

In what context is it ok to use implicit coercion?

Answer 40

• Don’t useString()ortoString()inside${...}expressions in template literals.
• Feel free to use the unary+operator to convert strings to numbers.

Question 41

What is the result of
1 == true?

Answer 41

true

Question 42

What is the result of
3==true?

Answer 42

false

When comparing a boolean with any value,==coercestrueand
falseto their number equivalents, which are1and0

Question 43

What is the result of
0==false?

Answer 43

true

Question 44

What is the result of
‘1’ == true?

Answer 44

true

Question 45

What is the result of
undefined == null?

Answer 45

true

Question 46

if you have a value that may be null or undefined how can you test that in one step?

Answer 46

if (val == undefined) {
// do one thing
} else {
// do another thing
}

Question 47

What happens when comparing objects with ==

Answer 47

When both operands are objects,==behaves exactly like the===operator; that is, it considers two objects equal only when they’re the same object:

when one of the operands is an object and the other a primitive,==coerces the object to a primitive before making the comparison

Question 48

‘[object Object]’ == {}

Answer 48

true

Question 49

What happens when a number is compared with a string using==

Answer 49

the string is coerced into a number

Question 50

When a boolean is compared with any other value

Answer 50

it is coerced into a number and compared again using the==operator.

Question 51

result: ‘number ‘ + 1

Answer 51

‘number 1’

whenever one of the operands of the+operator is a string, the other operand is also coerced to a string and concatenated with the string:

Question 52

’’ + undefined

Answer 52

‘undefined’

Question 53

’’ + true

Answer 53

‘true’

Question 54

’’ + [1, 2, 3]

Answer 54

‘1,2,3’

Question 55

’’ + {}

Answer 55

‘[object Object]’

Question 56

1 + undefined;

Answer 56

// NaN

Question 57

null + false;

Answer 57

// 0

Question 58

1 + true;

Answer 58

2

Question 59

[1] + 2;

Answer 59

12

Question 60

[1, 2] + 3;

Answer 60

// “1,23”

Question 61

[] + true;

Answer 61

“true”

Question 62

How are The relational operators,<,>,<=, and>= defined

Answer 62

They are defined for numbers (numeric comparison) and strings (lexicographic order).

Question 63

‘b’ > ‘a’

Answer 63

true

Question 64

1 < 2

Answer 64

true

Question 65

How does JS choose lexicographic or numeric comparison?

Answer 65

When both operands are strings, JavaScript compares them lexicographically. Otherwise, JavaScript converts both operands to numbers before comparing them.

Question 66

11 > ‘9’;

Answer 66

// true – ‘9’ is coerced to 9

Question 67

123 > ‘a’;

Answer 67

// false – ‘a’ is coerced to NaN; any comparison with NaN is false

Question 68

true > null;

Answer 68

// true – becomes 1 > 0

Question 69

undefined >= 1;

Answer 69

// false – becomes NaN >= 1

Question 70

null <= false;

Answer 70

// true – becomes 0 <= 0

Question 71

What is the output of
console.log([1, 2, 3] + [4, 5]);

Answer 71

1,2,34,5