Merge Sort JavaScript Implementation

Question

I'm doing a course on Khan Academy on Algorithms.
I usually try to figure out the examples by myself but this time I am really not getting it. The exercise is at: Khan Academy Merge Sort Exercise.
So I'm asking a kind person to please resolve this exercise for me, because I'm stuck and it is the first time that I can't implement something. I'm sure that I will understand the algorithm (I think I do, but it gives me errors on implementing, so apparently I'm not understanding) after seem the resolution.
Here is the code that I have done so far:

// Takes in an array that has two sorted subarrays,
//  from [p..q] and [q+1..r], and merges the array
var merge = function(array, p, q, r) {
    // This code has been purposefully obfuscated,
    //  as you'll write it yourself in next challenge.
    var a=[],b=[],c=p,d,e;for(d=0;c<=q;d++,c++){a[d]=array[c];}for(e=0;c<=r;e++,c++){b[e]=array[c];}c=p;for(e=d=0;d<a.length&&e<b.length;){if(a[d]<b[e]){array[c]=a[d];d++;} else {array[c]=b[e]; e++;}c++; }for(;d<a.length;){array[c]=a[d];d++;c++;}for(;e<b.length;){array[c]=b[e];e++;c++;}
};


// Takes in an array and recursively merge sorts it
var mergeSort = function(array, p, r) {
    if(r > 1) {
        var q = Math.floor((p + r) / 2);
        mergeSort(array,p,q);
        mergeSort(array,q+1,r);
        merge(array, p, q, r);
    }

};

var array = [14, 7, 3, 12, 9, 11, 6, 2];
console.log(''+array);
mergeSort(array, 0, array.length-1);
console.log("Array after sorting: " + array);

// Takes in an array that has two sorted subarrays,
    //  from [p..q] and [q+1..r], and merges the array
    var merge = function(array, p, q, r) {
        // This code has been purposefully obfuscated,
        //  as you'll write it yourself in next challenge.
        var a=[],b=[],c=p,d,e;for(d=0;c<=q;d++,c++){a[d]=array[c];}for(e=0;c<=r;e++,c++){b[e]=array[c];}c=p;for(e=d=0;d<a.length&&e<b.length;){if(a[d]<b[e]){array[c]=a[d];d++;} else {array[c]=b[e]; e++;}c++; }for(;d<a.length;){array[c]=a[d];d++;c++;}for(;e<b.length;){array[c]=b[e];e++;c++;}
    };
    
    
    // Takes in an array and recursively merge sorts it
    var mergeSort = function(array, p, r) {
        if(r > 1) {
            var q = Math.floor((p + r) / 2);
            mergeSort(array,p,q);
            mergeSort(array,q+1,r);
            merge(array, p, q, r);
        }
        
    };
    
    var array = [14, 7, 3, 12, 9, 11, 6, 2];
    console.log(''+array);
    mergeSort(array, 0, array.length-1);
    console.log("Array after sorting: " + array);

Answer 1

It has something to do with the if condition

what the if condition achieves is to check that the r that is end of array is greater that p start of the array.

I'm not sure what r > 1 is trying to do. hence it doesn't get satisfied and executes recursively untill it runs out of stack space

// Takes in an array that has two sorted subarrays,
//  from [p..q] and [q+1..r], and merges the array
var merge = function(array, p, q, r) {
  // This code has been purposefully obfuscated,
  //  as you'll write it yourself in next challenge.
  var a = [],
    b = [],
    c = p,
    d, e;
  for (d = 0; c <= q; d++, c++) {
    a[d] = array[c];
  }
  for (e = 0; c <= r; e++, c++) {
    b[e] = array[c];
  }
  c = p;
  for (e = d = 0; d < a.length && e < b.length;) {
    if (a[d] < b[e]) {
      array[c] = a[d];
      d++;
    } else {
      array[c] = b[e];
      e++;
    }
    c++;
  }
  for (; d < a.length;) {
    array[c] = a[d];
    d++;
    c++;
  }
  for (; e < b.length;) {
    array[c] = b[e];
    e++;
    c++;
  }
};


// Takes in an array and recursively merge sorts it
var mergeSort = function(array, p, r) {
  if (r > p) {
    var q = Math.floor((p + r) / 2);
    mergeSort(array, p, q);
    mergeSort(array, q + 1, r);
    merge(array, p, q, r);
  }

};

var array = [14, 7, 3, 12, 9, 11, 6, 2];
console.log('' + array);
mergeSort(array, 0, array.length - 1);
console.log("Array after sorting: " + array);