Merge Sort Algorithm with Javascript (CommonJS)

index.js

const { Merge } = require('./Merge)

const a = [15, 5, 24, 8, 1, 3, 16, 10, 20]

Merge.display(a) // output: [15, 5, 24, 8, 1, 3, 16, 10, 20]
Merge.sort(a, 0, a.length - 1)
Merge.display(a) // output: [1, 3, 5, 8, 10, 15, 16, 20, 24]

Merge.js

class Merge {
  static sort(a, lb, ub) {
    if (lb < ub) {
      const mid = parseInt((lb + ub) / 2)
      Merge.sort(a, lb, mid)
      Merge.sort(a, mid + 1, ub)
      Merge.concat(a, lb, mid, ub)
    }
  }

  static concat(a, lb, mid, ub) {
    let i = lb
    let j = mid + 1
    let k = lb

    const b = []

    while (i <= mid && j <= ub) {
      if (a[i] <= a[j]) {
        b[k] = a[i++]
      } else {
        b[k] = a[j++]
      }
      k++
    }

    if (i > mid) {
      while (j <= ub) {
        b[k++] = a[j++]
      }
    } else {
      while (i <= mid) {
        b[k++] = a[i++]
      }
    }

    for (k = lb; k <= ub; k++) {
      a[k] = b[k]
    }
  }

  static display(a) {
    const data = a.join(', ')
    console.log(`[${data}]`)
  }
}

module.exports = { Merge }

Merge.test.js

const { deepStrictEqual } = require('assert')

;
(() => {
    const expected  = [1, 3, 5, 8, 10, 15, 16, 20, 24]
    
    // Should be able apply merge sort with values out of order
    {
        const a = [15, 5, 24, 8, 1, 3, 16, 10, 20]
        
        Merge.sort(a, 0, a.length - 1)
        
        deepStrictEqual(a, expected)
    }
    
    // Should be able apply merge sort with values already sorted
    {
        const a = [1, 3, 5, 8, 10, 15, 16, 20, 24]
        
        Merge.sort(a, 0, a.length - 1)
        
        deepStrictEqual(a, expected)
    }
    
    // Should be able apply merge sort with values inversed
    {
        const a =  [24, 20, 16, 15, 10, 8, 5, 3, 1]
        
        Merge.sort(a, 0, a.length - 1)
        
        deepStrictEqual(a, expected)
    }
    
    // Should be able apply merge sort with values repeated
    {
        const a = [7, 7, 127, 500, 127, 7, 7, 8, 8, 8, 4, 4, 0, 0, 2, 2, 2, 5, 5, 5]
        const expected = [0, 0, 2, 2, 2, 4, 4, 5, 5, 5, 7, 7, 7, 7, 8, 8, 8, 127, 127, 500]
        
        Merge.sort(a, 0, a.length - 1)
        
        deepStrictEqual(a, expected)
    }
})()

Add tests to Merge Sort Algorithm

• Apply merge sort with values out of order.
• Apply merge sort with values already sorted.
• Apply merge sort with values inversed.
• Apply merge sort with values repeated.