TS2532: Object is possibly undefined

[Dirain1700]

Bug Report

🔎 Search Terms

TS2532, possibly undefined

🕗 Version & Regression Information

typescript@4.6.2
@types/node@17.0.33

Node.js v16.14.2
npm v8.1.2

⏯ Playground Link

Playground link with relevant code

💻 Code

//@target: esnext
//@moduleResolution: node
//@module: commonjs
declare var process: any;
declare var Console: any;
(() => {
    const arg: string = process.argv[2]!;
    const arr: string[] = process.argv;
    let info: string | undefined = undefined;

    info = arg;

    if (info === undefined) {
        console.log([]);
        return;
    }

    console.log(arr.find((e) => e === info));// No error
    console.log(arr.find((e) => e.length === info.length));// Error: TS2532: Object is possibly undefined
    console.log(info);// No error (This is correct)
    console.log(info.length);// No error
})();

Output

"use strict";
(() => {
    const arg = process.argv[2];
    const arr = process.argv;
    let info = undefined;
    info = arg;
    if (info === undefined) {
        console.log([]);
        return;
    }
    console.log(arr.find((e) => e === info)); // No error
    console.log(arr.find((e) => e.length === info.length)); // Error: TS2532: Object is possibly undefined
    console.log(info); // No error (This is correct)
    console.log(info.length); // No error
})();

Compiler Options

{
  "compilerOptions": {
    "strict": true,
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "strictPropertyInitialization": true,
    "strictBindCallApply": true,
    "noImplicitThis": true,
    "noImplicitReturns": true,
    "alwaysStrict": true,
    "esModuleInterop": true,
    "declaration": true,
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "target": "Latest",
    "module": "CommonJS",
    "moduleResolution": "node"
  }
}

Playground Link: Provided

🙁 Actual behavior

Unable to compile TypeScript and compiler says "'info' is undefied".
if my code is wrong, I should get same error at line 18 and 21, but I didn't get that error.

🙂 Expected behavior

"info" is not undefined because already returned, so it should be compiled.

I don't know that cause.

[Josh-Cena]

Duplicate of #9998?

Narrowing is not preserved across callback boundaries. There's even a template designed for it which will get your issue auto-closed😆

[Dirain1700]

Should I add a note to that Issue?

[Josh-Cena]

No, there's no need.