Question

The answer is [2,2,2,2,2,2,2,2,2,2,2,2,2,2,]
Explain the code step by step and why the answer is above

const sum = (x,y) => x+y;
const add1 = (x) => sum(x,1);
const add2 = (x) => flip(x,1);
const flip = (x,y) => {y =[x, x=y][0]; return add1(x);}

alert([2,3,4,5,6,7,8,9,10,12,14,15,18,21].map(add2))

Answer 1

Let me explain this:

Map function is called on Array [2,3,4,5,6,7,8,9,10,12,14,15,18,21] with method "add2" on each element.

Let's pick an element one by one:

First element is 2 which is passed in "add2" method as argument, "add2" method is calling flip method with argument (2,1). Now flip method is doing the actual trick. in start x =2 , y =1

y = [x,x=y][0]

above line have three statements actually. x will be 1 and y will be assigned value of [2,1][0] which will be 2

1) first value of x is used as 2 .output will be [2,x=y][0].

2) then x =y assigned x to 1. output will be [2,1][0].

3) then y is assigned to 2 because [a,b] [0] will be a & [a,b][1] will be 1.

So now flip method will call "add1" method with parameter x which is having value 1 which in turn calls sum(1,1) which is giving output 2.

Second element is 3 which is passed in "add2" method as argument, "add2" method is calling flip method with argument (3,1). Now flip method is doing the actual trick. in start x =3 , y =1

y = [x,x=y][0]

above line have three statements actually. x will be 1 and y will be assigned value of [3,1][0] which will be 3.

1) first value of x is used as 3.output will be [3,x=y][0]

2) then x =y assigned x to 1. output will be [3,1][0].

3) then y is assigned to 3 because [3,1][0] will be 3.

So now flip method will call "add1" method with parameter x which is having value 1 which in turn calls sum(1,1) which is giving output 2.

so for each element of array, finally value of x is always 1 which is why you are getting output of 2 always.

//below screen shot is just for your testing and understanding when you change the value to y in flip method's final return statement

you can see the difference by just replacing x with y in flip method "return add1(y);" it will give you output as below:

I hope I am able to clarify your doubts. Comment me if you require further help.

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