doc: update fs.watchFile doc

[clement-nardi]

The current wording suggests to compare Date objects, which won't work.

[aduh95]

I mean, comparing Date objects does work in JavaScript:

new Date >= new Date; // true
new Date <= new Date; // true
new Date < new Date; // false
new Date > new Date; // false
new Date('1970-01-01') < new Date('2038-01-19'); // true
new Date('1970-01-01') > new Date('2038-01-19'); // false

// Equality on the other hand doesn't work
new Date == new Date // false
new Date('1970-01-01') == new Date('1970-01-01') // false

[clement-nardi]

Well, here the idea is to know whether a file has been modified by comparing modified times.
I think most people would use the inequality operator for this:

if (prev.mtime !== curr.mtime) {
    console.log("The file has been modified!")
}

which doesn't work.

Actually that's the root cause of a bug I just fixed.

[addaleax]

Keep in mind that "compare X and Y" does not mean "apply a JS comparison operator between X and Y"; for example, X.getTime() === Y.getTime() is a way to compare X and Y.

In any case, this can be sidestepped by just referring to curr.mtimeMs and prev.mtimeMs instead of curr.mtime and prev.mtime :)

[github-actions]

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