Repository navigation
TypeScript can't parse optional object when assigned to a variable #36510
Description
TypeScript Version: 3.7.5
Code
type A = { b?: { c?: number } }
const a: A = { b: {c: 123} };
const isSafe = a && a.b && a.b.c
// if (a && a.b && a.b.c) { // <= works
if (isSafe) { // <= breaks
console.log(a.b.c); // (TS 2532) Object is possibly 'undefined'.
}Expected behavior:
TS should check if isSafe protects against undefined
Actual behavior:
TS doesn't check isSafe
Output
"use strict";
const a = { b: { c: 123 } };
const isSafe = a && a.b && a.b.c;
// if (a && a.b && a.b.c) { // <= works
if (isSafe) { // <= breaks
console.log(a.b.c); // (TS 2532) Object is possibly 'undefined'.
}Compiler Options
{
"compilerOptions": {
"noImplicitAny": true,
"strictNullChecks": true,
"strictFunctionTypes": true,
"strictPropertyInitialization": true,
"strictBindCallApply": true,
"noImplicitThis": true,
"noImplicitReturns": true,
"useDefineForClassFields": false,
"alwaysStrict": true,
"allowUnreachableCode": false,
"allowUnusedLabels": false,
"downlevelIteration": false,
"noEmitHelpers": false,
"noLib": false,
"noStrictGenericChecks": false,
"noUnusedLocals": false,
"noUnusedParameters": false,
"esModuleInterop": true,
"preserveConstEnums": false,
"removeComments": false,
"skipLibCheck": false,
"checkJs": false,
"allowJs": false,
"declaration": true,
"experimentalDecorators": false,
"emitDecoratorMetadata": false,
"target": "ES2017",
"module": "ESNext"
}
}Playground Link: Provided
Activity
nmain100 commentedon Jan 29, 2020
Duplicate of #12184
typescript-bot commentedon Feb 6, 2020
This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.