I keep getting this error for my program: VM178 SortLib.js:71 Uncaught TypeError: Cannot read property 'length' of undefined

Question

I am trying to implement the Merge Sort Algorithm visually using HTML and Javascript. My output for the Merge Sort Implementation works as planned, but I keep on getting an error in my terminal window.

//Merge Sort Algorithm Implementation

//Function for dividing array into two sub problems
divide = (array) => {
    if (array.length < 2) {
        return array
    }
        const mid = Math.floor(array.length / 2)
        const smallOne = array.slice(0, mid)
        const smallTwo = array.slice(mid)
        return sort(divide(smallOne), divide(smallTwo))
    }

//Function for sorting array
sort = (smallOne, smallTwo) => {
    const sorted = []
    while (smallOne.length && smallTwo.length) {
        if (smallOne[0] <= smallTwo[0]) {
            sorted.push(smallOne.shift())
        } else {
            sorted.push(smallTwo.shift())
            }
        }
    const output = [...sorted, ...smallOne, ...smallTwo]
    console.log(output)
    return output
    }


//Functiom for merge sort
mergeSort = (array) => {
return sort(divide(array))
}

Here's a picture of my error in the console

Answer 1

You are getting the error because that smallTwo is undefined inside the sort function.

The Full error message is:

while (smallOne.length && smallTwo.length) {
                                       ^

TypeError: Cannot read property 'length' of undefined

Answer 2

Second parameter is missing

 mergeSort = (array) => { return sort(divide(array), ????) }

Answer 3

I think you can just call divide from mergeSort , As sort is expecting two variables and the sort call in mergeSort is called finally with already sorted output with a single parameter ..

 mergeSort = (array) => { return divide(array); }

Answer 4

you are calling the sort one more time after the array is being sorted

and the second array which is smallTwo become undefined

you can check if its undefined before your while iterator

if (!smallTwo) {
    smallTwo = []
}

that could solve you problem

or just send an empty array in your first call like this

mergeSort = (array) => {
return sort(divide(array), [])
}