False warnings for code when unreachable code

[gregbenz]

Bug Report

Sometimes for quick debugging, I add an early return to skip a bunch of code. However, this frequently causes new TypeScript warnings to be shown. These are not valid warnings, but rather a bug.

🔎 Search Terms

return, possibly undefined

🕗 Version & Regression Information

Have seen this since I started using TS

⏯ Playground Link

N/A

💻 Code

export async function TEST() {
	const obj: { notify?: { option1: boolean } } = {};
	const result = { notify: true };
	if (obj.notify) obj.notify.option1 = result.notify;

	return false; //The return causes TS to parse subsequent lines differently.
	if (obj.notify) obj.notify.option1 = result.notify; //Even though the if should address the concern, generates wavy red error: Object is possibly 'undefined'.ts(2532)
}

🙁 Actual behavior

The exact same line of code is treated differently if it happens to be unreachable (places after a return statement).

🙂 Expected behavior

Code should be treated the same, the return statement has no effect on possible pathways or variables that might create a valid concern.

tslint.json:

{
"defaultSeverity": "error",
"extends": ["tslint:recommended"],
"linterOptions": {
"exclude": ["bin", "../Other/."]
},
"rules": {
"no-async-without-await": false,
"no-floating-promises": true,
"await-promise": true,
"no-return-await": false,
"no-promise-as-boolean": true,
"promise-function-async": true,
"no-angle-bracket-type-assertion": true,
"prefer-for-of": true,
"triple-equals": true,
"no-shadowed-variable": true,
"static-this": true,
"use-isnan": true,
"deprecation": true,
"class-name": true,
"encoding": true,
"trailing-comma": false,
"comment-format": { "check-space": false },
"no-console": false,
"prefer-const": false,
"no-var-requires": false,
"no-trailing-whitespace": false,
"only-arrow-functions": false,
"object-literal-shorthand": false,
"semicolon": false,
"no-bitwise": true,
"no-debugger": false
}
}

tsconfig.json:

{
"compilerOptions": {
"noUnusedParameters": true,
"noFallthroughCasesInSwitch": true,
"strictNullChecks": true,
"strict": true,
"noImplicitReturns": true,
"resolveJsonModule": true,
"noImplicitAny": true,
"noImplicitThis": true,
"forceConsistentCasingInFileNames": true,
"outDir": "./dist/",
"sourceMap": true,
"target": "es2018",
"module": "esnext",
"moduleResolution": "node",
"lib": ["DOM", "DOM.Iterable", "ES6"],
"esModuleInterop": true,
"assumeChangesOnlyAffectDirectDependencies": true,
"jsx": "react"
},
"exclude": ["node_modules"]
}

[RyanCavanaugh]

Duplicate #26914

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.