Warn when Array.sort is used without a callback on non-string arrays

[iansan5653]

Search Terms

array.sort, sort, numeric array sort, alphabetic array sort

Suggestion

Give a warning when Array.sort is called without a callback on an array that is not of type string[].

Use Cases

By default Array.sort() sorts the array by the elements' UTF-16 code-point values after converting the array values to strings. This means that you'll get unexpected hidden results if you call sort on a numeric array (or any non-string array really). If you're intimately familiar with JavaScript, this is understood, but if you're coming from another language this would be surprising, unexpected, and hard to find.

Examples

// Don't warn - this will give the expected result
["a", "d", "b", "f", "bat"].sort() // -> ["a", "b", "bat", "d", "f"]

// Warn - this is almost definitely a mistake
[0, 1, 2, 3, 20, 10].sort() // -> [0, 1, 10, 2, 20, 3]

// Warn - this is most likely not the expected result
[1, true, false, 0].sort() // -> [0, 1, false, true]

// Don't warn - a callback was provided to handle numbers
[0, 1, 2, 3, 20, 10].sort((a, b) => a - b) // -> [0, 1, 2, 3, 10, 20]

Another example is microsoft/vscode#86440, where this mistake found its way into production code.

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• Not sure about this.
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

[ilogico]

Something like this:

interface Array<T> {
  sort(comparator: (a: T, b: T) => number): this;
  sort(this: Array<string>): this;
}

(the error message when the callback is omited is not very good though)
Technically, it's a breaking change. But I doubt it will break much legitimate code.
It will most likely reveal bugs.

[iansan5653]

@ilogico That's what I was thinking too, but I do think a more helpful error code would be needed because my first assumption on seeing that error would be that it's a bug with TypeScript and not with my code (since I know the comparator is optional).

[MartinJohns]

Related / duplicate of: #18286

[iansan5653]

Thanks @MartinJohns I'll close this and comment there