How does this code work?

Question

Code Omar Einea:
var a = (function func(num){
if(num==0) return 1;
return 1 + func(num-1);
})(3);
alert(a);

Answer 1

Understand the return here in recursion
Value is not returned to variable a all the time, it will return only after traceback of recursion

So assignment in a will happen only once.

Tracing the output will be like

1) when num=3
Func(3)
Return 1+func(2)

2) now num is 2
Func(2)
Return 1+func(1)

3)now num is 1
Func(1)
Return 1+func(0)

4)now num is 0 //limiting condition
Func(0)
Return 1 #this one is returned to the step 3's func(0)

Now value returned in step 3 is =>2

This 2 is returned to the step 2's
Func(1)

Now func(2) will return 3 to step 1's func(2)

Now that returned value 3 + 1 =>4

Thats how you obtained 4
now this 4 is assigned to variable a.

thats poping answer/returned value uses stack for storing, hence i told you about the stack.

Answer 2

You have wrote a program for recursive addition of 1,

Recursion is when, your function calls itself, and the if condition you specified is limiting condition for recursion
As you have wrote a function you can call it directly as,
var a = function func(para){}(arg);

Here the argument will replace the parameter provided, and will execute a function.

Coming back to recursion,
Once the program started the execution and encountered a return with a function call to itself, then JS interpreter push all the data into stack (a current result), and this cycle goes on continuously till the limiting condition is reached, once the limiting condition is encountered data is poped from stack in the reverse order it is put in (thats why stack is LIFO) and added 1 in the result
As you have said
Return 1+ func(num-1) //this one will be added.

Hence you will get a number incremented by 1 only...

You can try execution here
Hope that helped 😄

https://code.sololearn.com/W1XQ3uuX2LpY/?ref=app

Answer 3

I have modified the code to print the stack trace as well,
Values retuned will be get printed in console

Have a look at this code

https://code.sololearn.com/W1XQ3uuX2LpY/?ref=app

Answer 4

Good 👍 glad to hear that..!! Vasiliy

Answer 5

I think you wanted to say, "Your code has solved a number of questions" 😂

Answer 6

Aaditya Deshpande
Thank you!
I finally understood ☺:
https://code.sololearn.com/WNVjbi6Mz18l/?ref=app

Answer 7

Aaditya Deshpande
In general, I realized that this is a recursion, but I do not understand how output 4 is obtained.

1:
a = function func(3){
if(3==0) return 1;
return 1 + func(3-1);
}; => a+=2; ?

2:
a = function func(2){
if(2==0) return 1;
return 1 + func(2-1);
}; => a+=1; ?

3:
a = function func(1){
if(1==0) return 1;
return 1 + func(1-1);
}; => a+=1; ?

4:
a = function func(0){
if(0==0) return 1;
return 1 + func(0-1);
}; => a=4;

Answer 8

Aaditya Deshpande
Your code has spawned a number of questions.🙏

Answer 9

Aaditya Deshpande
No, your code solved one question and created others. 😂