What Does the '...' (Spread Syntax) Do in React Component Properties?

Understanding the Purpose of the Three Dots in React

When working with React, you may encounter the three dots (...), known as property spread notation. In this snippet:

<modal title="Modal heading" animation="{false}"></modal>

The "..." performs property spread, extracting the enumerable properties from this.props and distributing them as individual properties on the Modal element.

For instance, if this.props contains { a: 1, b: 2 }, then the above code is analogous to:

<modal a="{this.props.a}" b="{this.props.b}" title="Modal heading" animation="{false}"></modal>

Regardless of the exact content of this.props, spread notation ensures that any "own" properties within it are included.

Notably, children is considered an "own" property, so it will also be passed to the Modal component. This mechanism allows child elements to be nestled between the opening and closing tags of the parent component, which is a common and useful syntax for including children.

To illustrate:

class Example extends React.Component {
  render() {
    const { className, children } = this.props;
    return (
      <div classname="{className}">
      {children}
      </div>
    );
  }
}

In this example, Example accepts className and children as props. Child components or elements placed within Example will be assigned to the children prop.

Ultimately, property spread notation in React offers a convenient method to propagate properties from a parent component to its children, streamlining and simplifying the codebase.

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