React 是怎么知道 this.props 的？

Question

When I watch tutorials they try to read this.props without defining the term props anywhere. Is props a keyword? If not how does React know that it is props without defining it anywhere in the code?

Answer 1

No, props isn't a keyword. The React.Component constructor receives the props object (because React.createElement passes them to the component function as the first argument; JSX generates the calls to React.createElement ) and assigns props to the instance being created, like this:

constructor(props) {
//          ^^^^^−−−−−−−−−−− parameter
    this.props = props;
//  ^^^^^^^^^^^^^^^^^^−−−−−− assignment
    // ...
}

That's why if you create your own constructor, you have to pass the object you receive as the first parameter to super like this:

class MyComponent extends React.Component {
    constructor(props) {
       super(props);
//           ^^^^^^−−−−−−−−− passing them on to `super`
        // ...
    }
}

Answer 2

i don't know the technical details, (because i don't need to) but just know that whenever you use a react component (class based, or function based) some parameters get passed into the react component, and you guessed it, props got all of the parameters.

So if you wish to see what are the parameters in props you can just

console.log(this.props)

one of the most parameters that props has: are the ones you pass around yourself from a react component, to its child react component.