What is the logic behind these digits being printed from this array?

Question

var a = [1,3,4,6,8];
var b = [7,3,2,9,5];
var x = b.concat(a);

for (let i in x){
console.log(x[x[i]]);
}

console.log(x);

Edit: why does this print 4?

Edit2:

So the array looks like this after being concatenated
[ 7, 3, 2, 9, 5, 1, 3, 4, 6, 8 ]

But when I run the loop printing x[x[i]] the output is

4
9
2
8
1
3
9
5
3
6

I don't understand how that relates to the first array

Answer 1

After concatenation, x holds [1, 3, 4, 6, 8, 7, 3, 2, 9, 5]

Now in JavaScript arrays are internally stored as object, where index is the key and element at that index is the value
{"0": 1, "1": 3, "2": 4, "3": 6, "4": 8, "5": 7, "6": 3, "7": 2, "8": 9, "9": 5}

Now, you use in to iterate over objects
So...for(let i in x ) {
console.log(i);//is the key
console.lig(x[i]);//is the value of the key
}

Answer 2

You can think of x[x[3]] as
var index = x[3],
console.log(x[index]),

Answer 3

I've edited the question because I didn't understand why it prints 4

Answer 4

b.concat(a) means adding array a to the end on array b
https://code.sololearn.com/W25I2sDk6qMv/#js

Answer 5

So the array looks like this after being concatenated
[ 7, 3, 2, 9, 5, 1, 3, 4, 6, 8 ]

But when I run the loop printing x[x[i]] the output is

4
9
2
8
1
3
9
5
3
6

I don't understand how that relates to the first array

If I asked what would x[x[3]] print how would you figure out the answer is 8?

Answer 6

Thank you that finally clicked for me

Answer 7

You are welcome