Typescript：定义数组<t> object 内部</t>

Question

I'm coming from a JS background, and I'm learning TS.

I want to define an object with a single field, which is an array of strings, while taking advantage of strong typing.

let wrapper = {
  things: ['Thing 1']
}

wrapper.things[0] = 3; // wrong

Now, this works (and by works I mean it results in an error) because you can't assign a number to what has been inferred as an array of strings. What if I didn't want to provide an initial value to things , though? Something like this:

let wrapper = {
  things<String>: []
}

wrapper.things.push(3) // wrong
wrapper.things.push('abc') // correct

Answer 1

You can define a type.

interface Wrapper {
    things: string[];
}

const wrapper: Wrapper = { things: [] };

Or, if it isn't particularly reusable, inline it:

const wrapper: { things: string[] } = { things: [] };

Answer 2

I think you just have the order a little off. Try this:

const wrapper = {
  things: [] as string[]
};

or use an interface (probably more recommended) via the other answer.