Why TypeScript compiler does not give error when function returns undefined while function's re-CodePudding

Why TSC does not give error when function returns null or undefined while 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;
}

CodePudding user response：

You get no error when Type Checking compiler option strictNullChecks is off. Enabling the option will result in Typescript displaying the error for the functions add2 and add3.

You can read more about it: strictnullchecks-off and strictnullchecks-on

CodePudding user response：

add "strict":true under "compilerOptions" in tsconfig.json file.

CodePudding user response：

as @S.M mentioned above it is caused by strict flag indeed it is caused by strictNullChecks flag.

when I set

"strict": true,

"strictNullChecks": true,

TSC gives error as what I expect