readme.md

Intro

In this sample we will make use of hooks a cool concept introduced in React 16.7.0

Prerequisites

Install Node.js and npm if they are not already installed on your computer.

Verify that you are running at least node v6.x.x and npm 3.x.x by running node -v and npm -v in a terminal/console window. Older versions may produce errors.

Steps to build it

• Let's copy the code from sample 12_TableHttp.

• Let's install the dependencies.

npm install

• Now we are going to uninstall current version of react and react-dom:

npm uninstall react react-dom --save

• And install the 16.7 alfa version:

npm install [email protected] [email protected] --save

• We are going to move the current membersTable.tsx class based component to an stateless one (we will replace the current state using hooks).

• Let's start by cleaning up code and adding a hook to hold the members list.

./src/membersTable.tsx

- interface Props {
- }

- // We define members as a state (the compoment holding this will be a container
- // component)
- interface State {
-  members: Array<MemberEntity>
-}

- // Nice tsx guide: https://github.com/Microsoft/TypeScript/wiki/JSX
- export class MembersTableComponent extends React.Component<Props, State> {
+ export const MembersTableComponent = () => {
-  constructor(props: Props) {
-    super(props);
-    // set initial state
-    this.state = { members: [] };
-  }

+  const [members, setMembers] = React.useState([]);

-  // Standard react lifecycle function:
-  // https://facebook.github.io/react/docs/component-specs.html
-  public componentDidMount() {
+  const loadMembers = () => {
    memberAPI.getAllMembers().then((members) =>
-      this.setState({ members: members })
+       setMembers(members)
    );
  }

-  public render() {

    return (
      <div className="row">
        <h2> Members Page</h2>
        <table className="table">
          <thead>
            <MemberHead />
          </thead>
          <tbody>
            {
-              this.state.members.map((member: MemberEntity) =>
+              members.map((member: MemberEntity) =>
                <MemberRow key={member.id} member={member} />
              )
            }
          </tbody>
        </table>
      </div>
    );
-  }
}

• Now we have tetchy issue... componentDidMount we don't have this on hooks component, how can we do that? To do that we can make use of react hooks useEffect.

./src/membersTable.tsx

export const MembersTableComponent = () => {

  const [members, setMembers] = React.useState([]);

  const loadMembers = () => {
    memberAPI.getAllMembers().then((members) =>
      setMembers(members)
    );
  }

+ React.useEffect(() => {
+   loadMembers();
+ })

• That was nice, but what if we could be interested in reusing this hook?. We can extract it into a function:

./src/membersTable.tsx

+ function useMembers() {
+  const [members, setMembers] = React.useState([]);
+
+  const loadMembers = () => {
+    memberAPI.getAllMembers().then((members) =>
+      setMembers(members)
+    );
+  }
+
+  return {members, loadMembers };
+}

export const MembersTableComponent = () => {
+  const { members, loadMembers } = useMembers();
-  const [members, setMembers] = React.useState([]);

-  const loadMembers = () => {
-    memberAPI.getAllMembers().then((members) =>
-      setMembers(members)
-    );
-  }

  React.useEffect(() => {
    loadMembers();
  });

• Now if we ran this it will get ran on every rerender, in order to limit this we can pass an empty array as a second argument of useEffect, this tell React that you effect doesn't depend on any values from props or state, is it nevers needs to re-rerun.

  React.useEffect(() => {
    loadMembers();
-  });
+ },[]);

More info about hooks-effect: https://reactjs.org/docs/hooks-effect.html