Javascript Recursion Samples

1/* Stack: LIFO: “Last In, First Out”
2  function call() => an execution context gets placed on the execution stack
3
4  Execution Contexts:
5  STACK: [ global context, fn1 context, fn2 context, fn3 context ]
6
7  Execution Context
8    - Activation Object (parameters, variables and functions)
9    - 'this' pointer
10
11  callMe(); //last to be added, first to be called
12  STACK:
13    [ global context, fn1 context, fn2 context, fn3 context, callme context ]
14    [ global context, fn1 context, fn2 context, fn3 context ] <<
15    [ global context, fn1 context, fn2 context ] <<
16    [ global context, fn1 context ]
17    [ global context ]
18
19  Recursion:
20    Wait for return values from other execution contexts.
21    Divide-and-conquer approach to solve problems
22
23  A recursion without an exit condition will cause a Stack Overflow (no more memory on the stack), because we are adding execution contexts on the top of the stack
24*/
25
26// ------------------------------------------------------------------------------
27// product of all positive integers less than or equal to its argument.
28const factorial = (num) => {
29  debugger;
30  if (num === 0 || num === 1) {
31    return 1
32  } else {
33    return num * factorial(num - 1)
34  }
35}
36
37/*
38  Factorial Execution Contexts Stack State Overview
39  [ 5*fn(4), 4*fn(3), 3*fn(2), 2*fn(1), 1]
40  OK Stack pushes complete
41  Note: Stack is LIFO
42  (1) > (2x1) > (3x2) > (4x6) > (5x24)
43*/
44
45// const res = factorial(5);
46// console.log({res})
47
48
49// ------------------------------------------------------------------------------
50const fibonacci = function(num) {
51  if (num <= 1) {
52    return num
53  } else {
54    return fibonacci(num - 1) + fibonacci(num - 2)
55  }
56}
57fibonacci(5);
58
59/*
60  Factorial Execution Contexts Stack State Overview
61  [ 5*fn(4), 4*fn(3), 3*fn(2), 2*fn(1), 1]
62  OK Stack pushes complete
63  Note: Stack is LIFO
64  (1) > (2x1) > (3x2) > (4x6) > (5x24)
65*/