How do Typescript 2 apply non-empty types?

Question

I know that the general explanation is that the compiler performs static type checking, but what methods does the compiler specifically use to verify that unimaginable types accidentally come into play?

Answer 1

Uncertainty / Uncertainty Checking is simply changing the type of types from type models. As usual, all this happens during the type-checking phase, and nothing is in the emitted JavaScript to ensure this at runtime.

In any case, you can think of the type as a domain of values. For example, a domain booleanusually represents only two values trueand false. string- an unlimited domain that contains strings of the type "hello"and "world"and any other string.

TypeScript verifies that when a value is used at some type position, that value is in a domain of that type. For example, trueit is not in the domain number, so it is unacceptable to try to use truewhere it is expected number.

TypeScript , null undefined . , boolean : true, false, undefined null. , , undefined null , true false. , substr string null undefined, .

TypeScript , null undefined . null , string, string. string | null , string null.

Build 2016, 44:30, , , , , , , .

Answer 2

TypeScript ; , JavaScript. - :

let foo: { myProperty: string } = { myProperty: "g" }; // myProperty is non-nullable

foo["myProperty"] = undefined; // bypass type checker!