TypeScript Version: 4.0.0-beta
Search Terms:
- "unnecessary null check"
- "derived boolean null check"
Expected behavior:
When a created variable contains a null check, using that boolean should be sufficient for safe access to the variable.
Actual behavior:
TypeScript needs an additional null check.
Related Issues:
Code
export default function foo(a: {b: boolean} | undefined) {
const isNull = a == null;
if (isNull) {
return;
}
// Object is possibly 'undefined'.
return a.b
}Output
export default function foo(a) {
const isNull = a == null;
if (isNull) {
return;
}
return a.b;
}Compiler Options
{
"compilerOptions": {
"noImplicitAny": true,
"strictNullChecks": true,
"strictFunctionTypes": true,
"strictPropertyInitialization": true,
"strictBindCallApply": true,
"noImplicitThis": true,
"noImplicitReturns": true,
"alwaysStrict": true,
"esModuleInterop": true,
"declaration": true,
"experimentalDecorators": true,
"emitDecoratorMetadata": true,
"moduleResolution": 2,
"target": "ES2017",
"jsx": "React",
"module": "ESNext"
}
}Playground Link: Provided
TypeScript Version: 4.0.0-beta
Search Terms:
Expected behavior:
When a created variable contains a null check, using that boolean should be sufficient for safe access to the variable.
Actual behavior:
TypeScript needs an additional null check.
Related Issues:
Code
Output
Compiler Options
{ "compilerOptions": { "noImplicitAny": true, "strictNullChecks": true, "strictFunctionTypes": true, "strictPropertyInitialization": true, "strictBindCallApply": true, "noImplicitThis": true, "noImplicitReturns": true, "alwaysStrict": true, "esModuleInterop": true, "declaration": true, "experimentalDecorators": true, "emitDecoratorMetadata": true, "moduleResolution": 2, "target": "ES2017", "jsx": "React", "module": "ESNext" } }Playground Link: Provided