TypeScript中的“：”是什么意思？

Question

I'm knew to typescript/javascript but have experience with python/java/c++. Is this like the type hints in the newer versions of Python? Does ":" always mean a type hint or can it also mean something else?

Answer 1

TypeScript is a superset of ECMAScript, so first of all, the colon : has all the same meanings it has in ECMAScript:

• It is part of the syntax for the conditional operator condition? consequence1: consequence2 condition? consequence1: consequence2 which evaluates the condition and depending on its truthiness evaluates either consequence1 or consequence2 (but never both), and the value of the whole expression is the value of the consequence that was evaluated.
• It is part of the syntax for an object literal :

   const obj = { foo: 4, "bar": 8, ["ba" + "z"]: 15, } console.log(obj);

• It is an assignment property , part of the syntax for destructuring assignment :

   const obj = { foo: 16, bar: 23, baz: 42, } const { foo: frotz, baz: quux } = obj; console.log(frotz, quux);

• It is part of the syntax for a label :

   someLabel: for (let i = 0; i < 2; i++) { for (let j = 100; j < 102; j++) { console.log({ i, j }); continue someLabel; } }

But it also has additional meaning in TypeScript, where it is used for type annotations :

const i: number = 4711;
const s: string = "Hello";

function f(a: number, b: string): never

Note that these are not "type hints". They are type annotations . They aren't hinting at anything, they are strictly enforced.