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strictNullChecks safeguards against null and undefined, but not NaN #21279
Description
Code
// simple convertion
let n: number = Number("not-a-number") // could be NaN
// function that returns NaN
function couldBeNaN(x: any): number {
if(typeof x === "number"){
return x;
}
return NaN
}
n = couldBeNaN("not-a-number") // will return NaN Expected behavior:
A safeguard against NaN as there is for null and undefined.
// simple convertion
let n: number | NaN = Number("not-a-number") // enforced check
// function that returns NaN
function couldBeNaN(x: any): number | NaN {
if(typeof x === "number"){
return x;
}
return NaN
}
n = couldBeNaN("not-a-number") // will return NaN, but it's okay Hence NaN isn't a type in TypeScript, this isn't possible.
Actual behavior:
NaN passes as a regular number although it is the direct opposite (yes, I know it is defined as such in the ECMAScript-standard, but nonetheless, it almost always hits you unexpected).
Activity
RyanCavanaugh commentedon Jan 18, 2018
Strict null checks isn't about NaN because NaN isn't null (or undefined). If you'd like to write a suggestion proposal, please follow the guidelines for that.
typescript-bot commentedon Feb 1, 2018
Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.