ReactJS events - this.props.onSubmit(this.state....)

The following code snippet is from a simple Todo list which stores information on a local EOS blockchain and has a frontend web interface built on ReactJS. The question is related to ReactJS, specifically the event handler code snippet

saveTodo(e) {
  e.preventDefault();
  this.props.onSubmit(this.state.description)
  this.setState({ description: "" })
}

The full program can be found here...https://github.com/eosasia/eos-todo/blob/master/frontend/src/index.jsx

In the body of the event handler saveTodo(e), there is a line this.props.onSubmit(this.state.description). I would like to know what exactly is going on here?

I am new to ReactJS, and it looks to that the above line of code is somehow setting a property (props) by calling a built-in function onSubmit() with an argument retrieved from the state object. Is this correct? I don’t see how onSubmit() was assigned to props anywhere in this code, but somehow we are able to use it like so: this.props.onSubmit(this.state.description) …. What’s going on here?

Thank you kindly.

P.S. pardon the terminology. I'm not sure if "event handler" or "event listener" is the right word.

Solution

The TodoForm component takes a property "onSubmit".

That line is simply calling this property (that was passed to it by its parent) and passing in the description ( taken from the state of TodoForm ).

For example:

<TodoForm onSubmit={(description) => alert(description)} />