Javascript ... rest operator behavior using a new array value?

Question

I have the following code below, the value that is being passed in is 4, 1, 9, 14, 6 ,8 and the value which is assigned to newHeight is 1, 4, 6, 8, 9, 14. Insertion Sort sorts the array in ascending order.

var heightChecker = function(heights) {

    var sorted = [...heights];
    var newHeight = insertionSort(heights);
    var count = 0;
    
    for(var i = 0; i < newHeight.length; i++) {
        if(newHeight[i] !== sorted[i]) {
            count++;
        }
    }

    return count;
}

insertionSort sorts the array, and when i use this line of code

var sorted = [...height];

Then it returns the answer I was looking for which is 3. However when i change the code to be


 var heightChecker = function(heights) {

      var newHeight = insertionSort(heights);
      var count = 0;
      
      for(var i = 0; i < heights.length; i++) {
          if(newHeight[i] !== heights[i]) {
              count++;
          }
      }
  
      return count;
  }

It returns the answer as 0.

I am not understanding why it isn't the same answer, and after debugging and google searching, I still cannot find why.

Here is the insertion sort code

function insertionSort(inputArr) {
    let n = inputArr.length;
    for (let i = 1; i < n; i++) {
        // Choosing the first element in our unsorted subarray
        let current = inputArr[i];
        // The last element of our sorted subarray
        let j = i-1;
        while ((j > -1) && (current < inputArr[j])) {
            inputArr[j+1] = inputArr[j];
            j--;
        }
        inputArr[j+1] = current;
        console.log(inputArr);
    }
    return inputArr;
}

Could you also post back code from insertionSort function

jaswanth
– jaswanth

2020-09-17 04:27:20 +00:00
Commented Sep 17, 2020 at 4:27 — jaswanth
– jaswanth, Commented Sep 17, 2020 at 4:27
just added the insertionSort function code

Taner
– Taner

2020-09-17 05:27:21 +00:00
Commented Sep 17, 2020 at 5:27 — Taner
– Taner, Commented Sep 17, 2020 at 5:27

knittl · Accepted Answer · 2020-09-29 18:28:51Z

1

a = [...b] creates a copy of b, a = b only assigns a different name to your value (i.e. a second reference pointing to the same value).

let a = [1,2,3];
b = a;
c = [...a];
a[1] = 41; // modifies value of a AND b
b[1] = 42; // modifies value of a AND b
c[1] = 43; // only modifies value of c
console.log(a); // 1, 42, 3
console.log(b); // 1, 42, 3
console.log(c); // 1, 43, 3

or, with a function call:

function addNumber(array, number) {
  array.push(number);
}
let a = [1,2,3];
b = a;
c = [...a];
addNumber(b, 4); // now a = [1,2,3,4]; and b = [1,2,3,4] (=a); c = [1,2,3]
addNumber(c, 5); // still a = [1,2,3,4]; but c = [1,2,3,5]

edited Sep 29, 2020 at 18:28

answered Sep 17, 2020 at 5:32

knittl

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2 Comments

Taner Over a year ago

I just edited my code, With my new edits does your comment still hold true? Instead of assigning the parameter in the first function, I am just using the parameter in the loop.

knittl Over a year ago

I assume. Assigning an array to a diferent variable does not copy the array's contents, using the rest operator (or .slice) however does.

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