How is the answer 10?

Question

const arr = ['0', '1', '4', 'a', '9', 'c', '16'];
const my_obj = {
[Symbol.iterator]: function*() {
for(let index of arr) {
yield `${index}`;
}
}
};

const all = [...my_obj] /* Here you can replace the '[...my_obj]' with 'arr'. */
.map(i => parseInt(i, 10))
.map(Math.sqrt)
.filter((i) => i < 5) /* try changing the value of 5 to 4 see what happens.*/
.reduce((i, d) => i + d); /* comment this line while you are changing the value of the line above */

console.log(all);

Answer 1

Oh,ok.
Let's take the bottom part first replacing [...my_obj] with arr:
const all = arr ....
//map method takes a function argument and returns a new array containing the values of the original array using the function argument as mapper:
.map(i=>parseInt(i,10)) // i here is reffering to the "arr" values. this returns an array containing base10(second arg of parseInt) numeric representations of every arr values. Our result is [0,1,4, NaN,9,NaN,16] so far.

.map(Math.sqrt) // we map the previous result using ²√. Our result is [0,1,2, NaN,3,NaN,4] now.

.filter( i=> i<5 ) //filter returns a new array containing only the values that make the argument function return true. Our result is [0,1,2,3,4] now because NaN < 5 is false.

.reduce((i,d)=> i+d) //reduce returns the result of the argument function applied from left to right.
0+1= 1, 1+2=3, 3+3 = 6, 6 + 4 = 10 and that's our final result.

All above methods are available on Arrays only.

Answer 2

What exactly you don't understand? Which part?

Answer 3

[Symbol.iterator] is a computed property that expects an interator(or generator) as value. The yielded values of that iterator are exhausted by "for of" loops and spread operator.

For example every array has a custom Symbol.iterator that yields the arrays values one by one:
for(let index of arr)
//Here index gets assigned to the next value of the arr iterator (starting from left to right).

If we want to use that functionality in non-array objects we need to define the iterator by our own.

Thus when we use [...my_obj] we are spreading the results of the generator until it's exhausted. That results are the yielded out by the "for of" loop or what is the same: the string(check the template literal ${} is enclosing "index") representation of the "arr" values.

Answer 4

Shipra Waghmare 😂 Lol.
You are welcome i'm glad to help.

Answer 5

The whole code

Answer 6

Thank you so much Kevin🤩🤩 you could be a programming tutor.