how to avoid incorrect comparison function technically?

Question

[2,4,1,7,5].sort((a, b)=>a>b)  // wrong
[2,4,1,7,5].sort((a, b)=>a-b)  // correct

If I haven't used this function for several years, there will be a high possibility for me to use it in the wrong way.

Is there a technical means to avoid it?

Do you understand how it works? That will help you to avoid writing incorrect code. — Kobe, Jul 01 '19 at 08:00
`sort` needs a number to be returned in callback (negative, positive or 0). I don't think there's a need for technical means to avoid it... Quick MDN reference would help you. https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Array/sort — Walk, Jul 01 '19 at 08:01
true, i thought the OP was more on distinguishing what the return values need to be for the asc/desc order.. but it was an assumption — Gabriele Petrioli, Jul 01 '19 at 08:04
[Sorting in JavaScript: Shouldn't returning a boolean be enough for a comparison function?](https://stackoverflow.com/questions/24080785) — adiga, Jul 01 '19 at 08:05

score 1 · Answer 1 · answered Jul 01 '19 at 08:18

If you think you're very likely to write code like your first example and you really want to avoid it, I can think of two ways:

Write a plugin for ESLint or similar that looks to see if the sort callback returns the result of a comparison operation.
Write a development-time-only wrapper for sort that throws an error if the callback doesn't return a number. But I probably wouldn't include it in the production version, just during development.

#2 looks something like this:

const sort = Array.prototype.sort;
Array.prototype.sort = function(callback) {
    return sort.call(this, (a, b) => {
        const rv = callback(a, b);
        if (typeof rv !== "number") {
            throw new Error("Array.prototype.sort callback must return a number");
        }
        return rv;
    });
};

Live Example:

const sort = Array.prototype.sort;
Array.prototype.sort = function(callback) {
    return sort.call(this, (a, b) => {
        const rv = callback(a, b);
        if (typeof rv !== "number") {
            throw new Error("Array.prototype.sort callback must return a number");
        }
        return rv;
    });
};

try {
  console.log([2,4,1,7,5].sort((a, b)=>a>b));
} catch (e1) {
  console.error(e1.message);
}

try {
  console.log([2,4,1,7,5].sort((a, b)=>a-b));
} catch (e2) {
  console.error(e2.message);
}

how to avoid incorrect comparison function technically?

1 Answers1