JavaScript Quiz 02


What do the following code blocks print?

1)

var foo = 42;
function setVar() {
    foo = 21;
}
setVar();
console.log(foo);
a b c d e
foo 42 21 undefined error

2)

var foo = 42;
function setVar() {
    var foo = 21;
}
setVar();
console.log(foo);
a b c d e
foo 42 21 undefined error

3)

var foo = 42;
function setVar() {
    var foo = 21;
    console.log(foo);
}
setVar();
a b c d e
foo 42 21 undefined error

4)

var foo = 42;
function setVar() {
    console.log(foo);
    var foo = 21;
}
setVar();
a b c d e
foo 42 21 undefined error

5)

foo = 42;
function setVar() {
    console.log(foo);
    var foo = 21;
}
setVar();
a b c d e
foo 42 21 undefined error

6)

var arr = [1, 2, 3];
console.log(arr);
a b c d e f
[1, 2, 3] [1] 1 [1,2] undefined error

7)

var arr = [1, 2, 3];
arr.length = 1;
console.log(arr);
a b c d e f
[1, 2, 3] [1] 1 [1,2] undefined error

8)

var arr = [1, 2, 3];
arr.length = 1;
console.log(arr[1]);
a b c d e f
[1, 2, 3] [1] 1 [1,2] undefined error

9)

console.log("" == false)

a b c d
true false undefined error

10)

console.log("" == 0)

a b c d
true false undefined error

11)

console.log(0 == "0")

a b c d
true false undefined error

12)

console.log("" == "0")

a b c d
true false undefined error

13)

console.log("" === false)

a b c d
true false undefined error

14)

console.log("" === 0)

a b c d
true false undefined error

15)

console.log(0 === "0")

a b c d
true false undefined error

16)

console.log("" === "0")

a b c d
true false undefined error

17)

console.log(10 == '+10')

a b c d
true false undefined error

18)

console.log(10 == '010')

a b c d
true false undefined error

19)

console.log(10 == +10)

a b c d
true false undefined error

20)

console.log(10 == 010)

a b c d
true false undefined error

21)

console.log(undefined == null)

a b c d
true false undefined error

22)

console.log(undefined === null)

a b c d
true false undefined error

23)

console.log(!!0)

a b c d
true false undefined error

24)

console.log(!!false)

a b c d
true false undefined error

25)

console.log(!!'')

a b c d
true false undefined error

26)

console.log(!!undefined)

a b c d
true false undefined error

27)

var options = ['test1', 'test2', 'test3'];
console.log(options[0]);
(options || []).forEach((el) => console.log(el));
a b c d
test1\ntest2\ntest3 test1\ntest1\ntest2\ntest3 undefined error

28)

var options = ['t1', 't2', 't3']
console.log(options[0])
(options || []).forEach((el) => console.log(el))
a b c d
t1\nt2\nt3 t1\nt1\nt2\nt3 undefined error

29)

Should you ever use eval()?

a b
Yes No

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