Why does TypeScript not show an error when a function returns null or undefined while the function's return type is number.
//gives error
//Error : A function whose declared type is neither 'void' nor 'any' must return a value.ts(2355)
function add1(a: number, b: number): number {}
// no error
function add2(a: number, b: number): number {
return undefined;
}
// no error
function add3(a: number, b: number): number {
return null;
}
When the compiler option strictNullChecks is turned off, no errors are encountered during Type Checking. However, enabling this option will prompt Typescript to display errors for the functions add2 and add3.
To learn more about this, you can visit: strictnullchecks-off and strictnullchecks-on
To make your TypeScript compile more strict, insert "strict":true within the "compilerOptions" section of tsconfig.json.
As mentioned by @S.M earlier, the issue is triggered by the presence of the strict flag as well as the strictNullChecks flag.
Whenever I configure it like this:
"strict": true,
or like this:
"strictNullChecks": true,
TypeScript Compiler (TSC) will throw an error, which is exactly what I anticipate.
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