Typescript Array accepts wrong type

Question

I would expect the following code to fail to transpile, as B should not be a valid type for array.push. What am I missing?

class A {};
class B {};
const arr: A[] = [];
arr.push(new B());

A and B are structurally the same, that's why TypeScript accepts it: typescriptlang.org/docs/handbook/type-compatibility.html — UnholySheep
– UnholySheep, Commented Aug 29, 2018 at 17:07
Here's a helpful answer on S.O. stackoverflow.com/a/39562956/831878 — Ray Toal
– Ray Toal, Commented Aug 29, 2018 at 17:08

Explosion Pills · Accepted Answer · 2018-08-29 17:08:36Z

6

TypeScript uses structural compatibility to determine type compatibility. The classes are structurally compatible since they have the same properties (empty object).

See: https://www.typescriptlang.org/docs/handbook/type-compatibility.html

answered Aug 29, 2018 at 17:08

Explosion Pills

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