How to React "hooking" into Lifecyle Methods

Let's learn about useEffect hook

The useEffect hook is the combination of componentDidMount, componentDidUpdate and componentWillUnmount class lifecycle methods. This hook is the ideal place to setup listener, fetching data from API and removing listeners before component is removed from the DOM.

useEffect function is like saying, “Hi React, please do this thing after you render. ALWAYS.”

Let’s look at an example of useEffect in comparison with class lifecycle methods. Normally in class component, we write this kind of code:

class Example extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      role: 'web developer',
      name: 'Nathan',
    };
  }

  componentDidMount() {
    console.log(
      `didMount: Hello I'm ${this.state.name} and I'm a ${this.state.role}`
    );
  }

  componentDidUpdate() {
    console.log(
      `didUpdate: Hello I'm ${this.state.name} and I'm a ${this.state.role}`
    );
  }

  render() {
    return (
      <div>
        <p>{`Hello I'm ${this.state.name} and I'm a ${this.state.role}`}</p>
        <button
          onClick={() =>
            this.setState({ name: 'Gary', role: 'data scientist' })
          }
        >
          Change me
        </button>
      </div>
    );
  }
}

Since componentDidMount is run only once when the component is inserted into the DOM tree structure, subsequent render won’t trigger the method anymore. In order to do run something on each render, you need to use componentDidUpdate method.

Using useEffect hook is like having both componentDidMount and componentDidUpdate in one single method, since useEffect runs on every render. It accepts two arguments:

1. (mandatory) A function to run on every render
2. (optional) An array of state variables to watch for changes. useEffect will be skipped if none of the variables are updated.

Rewriting the above class into function component would look like this:

const Example = props => {
  const [name, setName] = useState('Nathan');
  const [role, setRole] = useState('web developer');

  useEffect(() => {
    console.log(`Hello I'm ${name} and I'm a ${role}`);
  });

  return (
    <div>
      <p>{`Hello I'm ${name} and I'm a ${role}`}</p>
      <button
        onClick={() => {
          setName('Gary');
          setRole('data scientist')
          }}>
        Change me
      </button>
    </div>
  )
}

Note: If you’re confused with the useState hook above, please refer to my useState introduction

The function component we just write will run the function inside of useEffect function on each render. Now this isn’t optimal because the state won’t be updated after the first click. This is where useEffect second argument come into play.

useEffect(() => {
    console.log(`Hello I'm ${name} and I'm a ${role}`);
  }, [name, role] );

By adding the array above, React will skip running the console.log method when there is no change to the state variables.

The componentWillUnmount and skipping componentDidUpdate part

You might have some code that need to run when the component will be removed from the DOM tree. In useEffect hook, you can specify a componentWillUnmount method by returning a function from the first argument. Here is an example:

useEffect(() => {
    console.log(`Hello I'm ${name} and I'm a ${role}`);

    return () => { console.log("componentWillUnmount"); }
  }, [name, role] );

Since componentWillUnmount is used for cleaning whatever left behind by your component, it’s really hard to give some practical example. But one example might be when using third party library like C3.js from Ashley Wilson

We can rewrite his code from this:

componentDidMount () {
  this._initGraph();
}

componentWillUnmount () {
  this.graph = this.graph.destroy();
}

into this:

useEffect(() => {
    this._initGraph();

    return () => { this.graph = this.graph.destroy(); }
  }, [] );

Do you wonder why we pass an empty array in the second argument? That’s because we want the hook to run this._initGraph() only once on didMount. You can pass an empty array [] to tell React that this component never re-render.

Conclusion

useEffect is the function component way to create lifecycle methods, and in the spirit of React hooks, it does make React code cleaner and use fewer lines of code.

More about React:

• React useState hook introduction
• How to code AJAX call in React?
• Understanding React Controlled Components
• React Props vs State

Original article source at: https://sebhastian.com/

#react #hooks #useeffect 

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How to React "hooking" into Lifecyle Methods

Let's learn about useEffect hook

The useEffect hook is the combination of componentDidMount, componentDidUpdate and componentWillUnmount class lifecycle methods. This hook is the ideal place to setup listener, fetching data from API and removing listeners before component is removed from the DOM.

useEffect function is like saying, “Hi React, please do this thing after you render. ALWAYS.”

Let’s look at an example of useEffect in comparison with class lifecycle methods. Normally in class component, we write this kind of code:

class Example extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      role: 'web developer',
      name: 'Nathan',
    };
  }

  componentDidMount() {
    console.log(
      `didMount: Hello I'm ${this.state.name} and I'm a ${this.state.role}`
    );
  }

  componentDidUpdate() {
    console.log(
      `didUpdate: Hello I'm ${this.state.name} and I'm a ${this.state.role}`
    );
  }

  render() {
    return (
      <div>
        <p>{`Hello I'm ${this.state.name} and I'm a ${this.state.role}`}</p>
        <button
          onClick={() =>
            this.setState({ name: 'Gary', role: 'data scientist' })
          }
        >
          Change me
        </button>
      </div>
    );
  }
}

Since componentDidMount is run only once when the component is inserted into the DOM tree structure, subsequent render won’t trigger the method anymore. In order to do run something on each render, you need to use componentDidUpdate method.

Using useEffect hook is like having both componentDidMount and componentDidUpdate in one single method, since useEffect runs on every render. It accepts two arguments:

1. (mandatory) A function to run on every render
2. (optional) An array of state variables to watch for changes. useEffect will be skipped if none of the variables are updated.

Rewriting the above class into function component would look like this:

const Example = props => {
  const [name, setName] = useState('Nathan');
  const [role, setRole] = useState('web developer');

  useEffect(() => {
    console.log(`Hello I'm ${name} and I'm a ${role}`);
  });

  return (
    <div>
      <p>{`Hello I'm ${name} and I'm a ${role}`}</p>
      <button
        onClick={() => {
          setName('Gary');
          setRole('data scientist')
          }}>
        Change me
      </button>
    </div>
  )
}

Note: If you’re confused with the useState hook above, please refer to my useState introduction

The function component we just write will run the function inside of useEffect function on each render. Now this isn’t optimal because the state won’t be updated after the first click. This is where useEffect second argument come into play.

useEffect(() => {
    console.log(`Hello I'm ${name} and I'm a ${role}`);
  }, [name, role] );

By adding the array above, React will skip running the console.log method when there is no change to the state variables.

The componentWillUnmount and skipping componentDidUpdate part

You might have some code that need to run when the component will be removed from the DOM tree. In useEffect hook, you can specify a componentWillUnmount method by returning a function from the first argument. Here is an example:

useEffect(() => {
    console.log(`Hello I'm ${name} and I'm a ${role}`);

    return () => { console.log("componentWillUnmount"); }
  }, [name, role] );

Since componentWillUnmount is used for cleaning whatever left behind by your component, it’s really hard to give some practical example. But one example might be when using third party library like C3.js from Ashley Wilson

We can rewrite his code from this:

componentDidMount () {
  this._initGraph();
}

componentWillUnmount () {
  this.graph = this.graph.destroy();
}

into this:

useEffect(() => {
    this._initGraph();

    return () => { this.graph = this.graph.destroy(); }
  }, [] );

Do you wonder why we pass an empty array in the second argument? That’s because we want the hook to run this._initGraph() only once on didMount. You can pass an empty array [] to tell React that this component never re-render.

Conclusion

useEffect is the function component way to create lifecycle methods, and in the spirit of React hooks, it does make React code cleaner and use fewer lines of code.

More about React:

• React useState hook introduction
• How to code AJAX call in React?
• Understanding React Controlled Components
• React Props vs State

Original article source at: https://sebhastian.com/

#react #hooks #useeffect 

“Hooking” your React frontend to your Flask API

Building out a React front end that calls onto a Flask API is very concise and easy, but very powerful. You have access to a very powerful back end in Flask that works very well with databases and storing information.

Flask is a microframework for Python, it is very easy to get started with and easy set up for a simple CRUD application. Flask is very simple to set up and create a small application with, but it is also easily scalable if you want to grow your application. You can read my previous blog post about creating an API in Flask here.

Starting a React app is very simple and user friendly, if you’re creating a single page application I recommend use using npx create-react-app my-app , if you’re looking for something more in depth I recommend looking at the React Docs.

For this blog I’m gonna create a small single page application that would hook to the Flask API through fetch calls allowing for GET request. After creating your React application with create-react-app make sure your Flask application is up and running, my Flask application will be open on http://localhost:5000.

#javascript #flask #python #react #api

React & Material UI: Creating a Pokedex (Part 4) - Hooking up to PokeApi

Part 4/5 of the React & Material UI Pokedex series

In this video:

• Removing the mock data references
• Hooking up our application with the PokeApi.co API to get real data
• Using MUI’s CircularProgress to show that the page is loading before the API has responded
• Handling not found Pokemon pages

Full code: https://github.com/AtotheY/YoutubePokedex

#react #javascript #web-development #programming #developer

Windows API Hooking and DLL Injection

This article is devoted to an approach for setting up local Windows API hooks. This article will also provide you with a DLL (dynamic link library) injection example: we will demonstrate how you can easily hook the system network adapter enumerator API call to manipulate the returned network adapter info.

Overview

Hooking covers a range of techniques for altering or augmenting the behavior of an operating system, application, or other software components by intercepting API function calls, messages, or events passed between software components. Code that handles such interception is called a hook.

At Plexteq, we develop complex networking and security applications for which we use low-level techniques such as hooking and injection. We would like to share our experience in this domain.

Some of the software applications that utilize hooks are tools for programming (e.g. debugging), antimalware, application security solutions, and monitoring tools. Malicious software often uses hooks as well; for example, to hide from the list of running processes or to intercept keypress events in order to steal sensitive inputs such as passwords, credit card data, etc.

There are two main ways to modify the behavior of an executable:

• through a source modification approach, which involves modifying an executable binary prior to application start through reverse engineering and patching. Executable signing is utilized to defend against this, preventing code that isn’t properly signed from being loaded.
• through runtime modification, which is implemented by the operating system’s APIs. Microsoft Windows provides appropriate harnesses for hooking the dialogs, buttons, menus, keyboard, mouse events, and various system calls.

API hooks can be divided into the following types:

• Local hooks: these influence only specific applications.
• Global hooks: these affect all system processes.

In this article, we’ll go over the hook technique for Windows that belongs to the local type done through a runtime modification using C/C++ and native APIs.

#security #injection #dll #hook #win32 api #api

Hooking Into The Angular Bootstrap Process

From this article you’ll learn how to use APP_INITIALIZER token and bootstrapModule to hook up into Angular’s initialization process.

Angular provides several mechanisms to hook into initialization process. This article explores them and shows how they can be used.

#angular #angular-bootstrap