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Array.prototype.map() allows assigning additional properties to an array of defined type #36354
Description
TypeScript Versions: from 3.5.1 to Nightly (issue not present in 3.3.3)
Search Terms: array map
Expected behavior: Third assignment should raise an error
Actual behavior: Assignment is allowed
Related Issues: No found any
Code
interface A {
a: 2
}
// 1. Correct: b property is not allowed in type A
const a: A = { a: 2, b: 8 }
// 2. Correct: b property is not allowed in type A
const other: A[] = [{ a: 2, b: 8 }]
// 3. Incorrect (no error): why is b property permitted here?
const array: A[] = [1, 2].map(i => ({ a: 2, b: 8 }))Output
"use strict";
// 1. Correct: b property is not allowed in type A
const a = { a: 2, b: 8 };
// 2. Correct: b property is not allowed in type A
const other = [{ a: 2, b: 8 }];
// 3. Incorrect (no error): why is b property permitted here?
const array = [1, 2].map(i => ({ a: 2, b: 8 }));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
jcalz commentedon Jan 22, 2020
Duplicate of #33158
The error in 3.3.3 is not the one you're looking for. That error is due to widening of
2tonumber; it has nothing to do with the presence of thebproperty. Even this errors in 3.3.3:In reality the error you expect is not happening because excess property checking only happens in very specific circumstances. See #33158 for more discussion. Good luck!
IllusionMH commentedon Jan 22, 2020
Or duplicate of #241
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.