Which type of value in the object as parameter of function. Why do not have the compilation errors?-CodePudding

I have gotten the next bunch of code.

const func: ( newState: { newState: number }) => void = ({ newState: newState }) => {
    console.log(newState);
}

For me, particularly interesting is the ({ newState: newState }) how is it work? Why can I write newState: newState in this situation, and no compilation errors?

CodePudding user response：

 const func: ( labeledParameter: { newState: number }) => void = ({ newState: test }) => {
    console.log(test);
}

func({newState: 12});

It's because the first newState is a label put on the parameters give to the function -> i renamed it labeledParameter in my sample

the object

{ newState: newState }

is an object with a property newState and as value a number

to call the function you should use

func({newState: 12});

CodePudding user response：

Let's understand by segregating the typescript and javascript portions in your code snippet.

TypeScript Portion

( newState: { newState: number }) => void

The portion above defines the type of the function which states that the function accepts an argument (which can be named anything, here it's named newState) that is an object with a key newState which is of type number and the void return type states that the function returns nothing.

JavaScript Portion

({ newState: newState }) => {
  console.log(newState);
}

And the portion above is the function definition where the argument is destructed in-place and the newState key has been aliased to newState, which is redundant, but works.

A more elaborate version of the above code snippet is as follows:

type Func = (newState: { newState: number }) => void

const func: Func = (arg) => {
    const { newState: renamed } = arg;
    console.log(renamed);
}

CodePudding user response：

const func: ( labeledParameter: { newState: number }) => void = ({ newState: test }) => { console.log(test); }

func({newState: 12}); It's because the first newState is a label put on the parameters give to the function -> i renamed it labeledParameter in my sample

the object

{ newState: newState } is an object with a property newState and as value a number

to call the function you should use

func({newState: 12});