{...this.state} spreads out the "own" enumerable properties in
props as discrete properties on the Modal element you're creating.
For instance, if this.props contained a: 1 and b: 2, then
<Modal {...this.state} title='Modal heading'>
would be the same as
<Modal a={this.state.a} b={this.state.b} title='Modal heading'>
let numberStore = [0, 1, 2];
let newNumber = 12;
numberStore = [...numberStore, newNumber];
[...iterableObj, '4', 'fünf', 6];