How to define default JavaScript sort callback function?-CodePudding

I'm attempting to create my own sort function (question Async version of sort function in JavaScript). I've taken merge sort function from Rosetta Code and make it async:

// based on: https://rosettacode.org/wiki/Sorting_algorithms/Merge_sort#JavaScript
async function mergeSort(fn, array) {
    if (array.length <= 1) {
        return array;
    }
    const mid = Math.floor(array.length / 2),
          left = array.slice(0, mid), right = array.slice(mid);
    await mergeSort(fn, left)
    await mergeSort(fn, right)
    let ia = 0, il = 0, ir = 0;
    while (il < left.length && ir < right.length) {
        array[ia  ] = (await fn(left[il], right[ir]) <= 0) ? left[il  ] : right[ir  ];
    }
    while (il < left.length) {
        array[ia  ] = left[il  ];
    }
    while (ir < right.length) {
        array[ia  ] = right[ir  ];
    }
    return array;
}

But I'm not sure how I can define default function fn to work the same as in JavaScript.

console.log([1, 2, 3, 10, 11, 100, 20].sort());

What should be the default sorting function to match those in the JavaScript engine? Should I convert numbers to strings and compare those? What is the proper implementation?

CodePudding user response：

Based on @jonrsharpe comments I was able to implement proper default function:

function defaultSortFn(a, b) {
    if (typeof a !== 'string') {
        a = String(a);
    }
    if (typeof b !== 'string') {
        b = String(b);
    }
    if (a < b) {
        return -1;
    }
    if (a > b) {
        return 1;
    }
    return 0;
}

that can be used in my sort:

Array.prototype.sort = function(fn = defaultSortFn) {
   return mergeSort(fn, this);
};

CodePudding user response：

The ECMAScript specification for Arra.prototype.sort mentions that the comparison (in absence of a comparator) involves:

e. Let xString be ? ToString(x).
f. Let yString be ? ToString(y).
g. Let xSmaller be ! IsLessThan(xString, yString, true).
h. If xSmaller is true, return -1