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Disallow case NaN, switch(NaN), indexOf(NaN), and lastIndexOf(NaN) (use-isnan) #1429

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feross opened this issue Sep 30, 2019 · 3 comments
Closed

Disallow case NaN, switch(NaN), indexOf(NaN), and lastIndexOf(NaN) (use-isnan) #1429

feross opened this issue Sep 30, 2019 · 3 comments
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accepted enhancement
Milestone
standard 16

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@feross
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feross commented Sep 30, 2019

https://eslint.org/docs/rules/use-isnan

This is a proposal to modify the use-isnan rule.

Current rule setting:

use-isnan: "error"

Proposed rule setting:

["error", {"enforceForSwitchCase": true}]

The switch statement internally uses the === comparison to match the expression's value to a case clause.
Therefore, it can never match case NaN. Also, switch(NaN) can never match a case clause.

Set "enforceForSwitchCase" to true if you want this rule to report case NaN and switch(NaN) in switch statements.

Examples of incorrect code for this rule with "enforceForSwitchCase" option set to true:

/*eslint use-isnan: ["error", {"enforceForSwitchCase": true}]*/

switch (foo) {
    case NaN:
        bar();
        break;
    case 1:
        baz();
        break;
    // ...
}

switch (NaN) {
    case a:
        bar();
        break;
    case b:
        baz();
        break;
    // ...
}

Examples of correct code for this rule with "enforceForSwitchCase" option set to true:

/*eslint use-isnan: ["error", {"enforceForSwitchCase": true}]*/

if (Number.isNaN(foo)) {
    bar();
} else {
    switch (foo) {
        case 1:
            baz();
            break;
        // ...
    }
}

if (Number.isNaN(a)) {
    bar();
} else if (Number.isNaN(b)) {
    baz();
} // ...
@feross feross added this to the standard 15 milestone Sep 30, 2019
@mightyiam
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Makes sense to me. If anyone is breaking by this that might be a bug rather than good code.

@feross feross modified the milestones: standard 15, standard 16 Oct 22, 2020
@feross
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feross commented Oct 29, 2020

No ecosystem impact. This is shipping in standard 16!

@feross feross changed the title Disallow case NaN and switch(NaN) (use-isnan) Disallow case NaN, switch(NaN), indexOf(NaN), and lastIndexOf(NaN) (use-isnan) Oct 29, 2020
@feross
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feross commented Oct 29, 2020

There's a new option: "enforceForIndexOf": true which disallows the use of indexOf and lastIndexOf methods with NaN. Let's enable it as well.

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Labels
accepted enhancement
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The Standard Project
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Milestone
standard 16
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@feross @mightyiam