… are called Spread Attributes which the name represents it allows an expression to be expanded.
var parts = ['two', 'three'];
var numbers = ['one', ...parts, 'four', 'five']; // ["one", "two", "three", "four", "five"]
Another example
//just assume we have an object like this:
var person= {
name: 'Alex',
age: 35
}
<Modal {...person} title='Modal heading' animation={false} />
is equal to
<Modal name={person.name} age={person.age} title='Modal heading' animation={false} />
