What do these three dots in React do?

Question

What does the ... do in this React (using JSX) code and what is it called?

Answer 1

This will be compiled into:

React.createElement(Modal, { ...this.props, title: "Modal heading", animation: false }, child0, child1, child2, ...)

where it gives more two properties title & animation beyond the props the host element has.

... is the ES6 operator called Spread.

See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax