can anyone explain these simple codes to me?

Question

var age = "15";
var message = (age < " year")?
true:
(age > "year")? false : true;
alert(message);

correct answer: true. Why?

let [learn, solo = "solo"] = "learn";
[solo, learn] = [learn, solo];
console.log(solo + learn);

a) le
b) learnsolo
c) Error
d) learn

output: le. Why?

Answer 1

>>>PART 1

I want to provide an complementary explanation on the first quiz.

First and foremost, the hungry alligator always eats the largest number. Have that in your mind!

1 oooo< eats the largest number 3
3 >oooo eats the largest number 1
Note: oooo< this is an alligator (= 

Let's break down the question:
var message = ("15" < " year") ? true: ("15" > "year") ? false: true;

>Part A
("15" < " year")

console.log("15" < " year"); //false

empty strings convert to 0 in a comparison. This is the same as this:
"15" < "0year" //false

console.log("15" < "year"); //true
We discover here that ("15" < " year") gets false. The ternary operator (condition ? truthy : falsy) returns the falsy condition:
("15" > "year").

Answer 2

;)

In Javascript, strings are treated mostly as arrays. So, this is the same as:
let [learn, solo = "solo"] = ["l", "e", "a", "r", "n"];

The string "solo" is an optional value for the variable solo; but it's overwritten by "e". So,
learn = "l", solo = "e"
Then, their values are switched, so solo + learn ("l" + "e") will be equal to "le"

Answer 3

>>>PART 2

> Part B
("15" > "year").
Just remember that letters are the big bosses who command over numbers when BOTH are STRINGS.
console.log("bossLetters" > "10"); //true

Different types (numbers vs strings) are always FALSE no matter the operator!

console.log("bossLetters" > 10); //false
console.log("bossLetters" < 10); //false

Finally we discover that  this part
("15" > "year") ? false: true;
The alligator is eating the number. Numbers are not great than strings/letters, right?.

That's why the second falsy part returns and we finish our assignment to message variable to: true.

Answer 4

Airree , thanks for this and your other answers, it helps a lot

Answer 5

Mofey , thanks for your help!