Lesson test: Making decisions

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Making decisions

1.[2p]
Why does this course tell you to use `===` and never `==`?

Loose equality is not transitive: 0 == "0" and 0 == "" are both true while "" == "0" is false, so arguments made with it can be invalid

Correct

== is slower to evaluate than ===

The answer is: Loose equality is not transitive: `0 == "0"` and `0 == ""` are both true while `"" == "0"` is false, so arguments made with it can be invalid

== was removed from the language standard

The answer is: Loose equality is not transitive: `0 == "0"` and `0 == ""` are both true while `"" == "0"` is false, so arguments made with it can be invalid

== cannot compare strings, only numbers

The answer is: Loose equality is not transitive: `0 == "0"` and `0 == ""` are both true while `"" == "0"` is false, so arguments made with it can be invalid

2.[2p]
What does `3 > 2 > 1` evaluate to? Write true or false.

CorrectNot quite: false

3.[3p]
Which of these values are falsy?

Select all that apply

The empty string ""

Correct

0

Correct

NaN

Correct

The string "0"

The answer is: The empty string `""`, `0`, `NaN`

The empty array []

The answer is: The empty string `""`, `0`, `NaN`

4.[3p]
Access is allowed when `loggedIn && !banned`. What is the correct condition for access denied?

!loggedIn || banned

Correct

!loggedIn && !banned

The answer is: `!loggedIn || banned`

!loggedIn && banned

The answer is: `!loggedIn || banned`

loggedIn || !banned

The answer is: `!loggedIn || banned`

5.[2p]
`const x = 0;` What number does `console.log(x ?? 10)` print?

CorrectNot quite: 0

6.[2p]
In `user && user.age >= 18`, short circuiting is what stops `user.age` being read when `user` is `undefined`.

True

Correct

False

The answer is: True

7.[2p]
A parcel costs £3 under 1 kg, £5 under 5 kg, and £9 otherwise. Put the tests in the order the chain must use them.

return 9;
if (weight < 1) return 3;
if (weight < 5) return 5;

Show the answer

b, a, c

8.[3p]
Match each expression to the value it produces.

0 || "d"
0 ?? 10
null ?? 10
0 == "0"
"" == "0"

the number 0
the string "d"
true
the number 10
false

Show the answer

0 || "d": the string "d" 0 ?? 10: the number 0 null ?? 10: the number 10 0 == "0": true "" == "0": false

9.[2p]
What is the point of a guard clause?

The exceptional cases are handled and returned first, so the main path stays at zero indentation and every rejection is visible at a glance

Correct

It runs faster than a nested if

The answer is: The exceptional cases are handled and returned first, so the main path stays at zero indentation and every rejection is visible at a glance

It removes the need to check for undefined

The answer is: The exceptional cases are handled and returned first, so the main path stays at zero indentation and every rejection is visible at a glance

It allows a function to return more than one value

The answer is: The exceptional cases are handled and returned first, so the main path stays at zero indentation and every rejection is visible at a glance

1.[2p] Why does this course tell you to use === and never ==?

2.[2p] What does 3 > 2 > 1 evaluate to? Write true or false.

3.[3p] Which of these values are falsy?

4.[3p] Access is allowed when loggedIn && !banned. What is the correct condition for access denied?

5.[2p] const x = 0; What number does console.log(x ?? 10) print?

6.[2p] In user && user.age >= 18, short circuiting is what stops user.age being read when user is undefined.

7.[2p] A parcel costs £3 under 1 kg, £5 under 5 kg, and £9 otherwise. Put the tests in the order the chain must use them.

8.[3p] Match each expression to the value it produces.

9.[2p] What is the point of a guard clause?

1.[2p]
Why does this course tell you to use `===` and never `==`?

2.[2p]
What does `3 > 2 > 1` evaluate to? Write true or false.

3.[3p]
Which of these values are falsy?

4.[3p]
Access is allowed when `loggedIn && !banned`. What is the correct condition for access denied?

5.[2p]
`const x = 0;` What number does `console.log(x ?? 10)` print?

6.[2p]
In `user && user.age >= 18`, short circuiting is what stops `user.age` being read when `user` is `undefined`.

7.[2p]
A parcel costs £3 under 1 kg, £5 under 5 kg, and £9 otherwise. Put the tests in the order the chain must use them.

8.[3p]
Match each expression to the value it produces.

9.[2p]
What is the point of a guard clause?