Why I am not getting warnings about StrictNullChecks in typescript

Question

I have the following code in typescript:

interface Member {
    name: string,
    age?: number
}

class Person implements Member {
    name: string;
    constructor(name: string ){
        this.name=name;
    }
}

function bar(person: Member) {
    return "Hello, " + person.name + " " + person.age;
}

let person = new Person("John");
console.log(bar(person));

I am supposed to get Object is possibly 'undefined' warning inside bar function when i declare person.age since not every Member can have age.

my typescript config looks like this:

{
  "compilerOptions": {
    "module": "commonjs",
    "target": "es5",
    "sourceMap": true,
    "strictNullChecks": true,
    "outDir": "./built"
  },
  "include": [
    "./src/**/*"
  ],
  "exclude": [
    "node_modules"
  ]
}

Any idea why this is not working for me? I am using WebStorm Editor!

Answer 1

Turn on "strict": true, in the tsconfig.json to enable this warning.

Or if you don't want all the strict options you in need:

"strictNullChecks": true,
"strictPropertyInitialization": true,

See the documentation for more information

--strictNullCheck:

In strict null checking mode, the null and undefined values are not in the domain of every type and are only assignable to themselves and any (the one exception being that undefined is also assignable to void).

--strictPropertyInitialization

Ensure non-undefined class properties are initialized in the constructor. This option requires --strictNullChecks be enabled in order to take effect.

The second one is the one you want (but needs strictNullChecks to work)

Btw, as @jayasai amerineni mentions, your example shouldn't trigger this warning.