Javascript Class Vs Function

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React-js is a JavaScript framework that allows developers to encapsulate code to make it more reusable. These encapsulated code snippets are called components . They can maintain their logic and state without interfering with what’s going on in Model Object document (DOM) .

Abstracting parts of your website into these smaller, smaller components to transfer data allows your code to become reusable and DRY ( D on’t R repeat Y us). There are two main types of components you will encounter in React: functional and class components


At a very high level, components of . react are basically JavaScript functions that take props as a parameter and return an React elements that basically describe what should be on the screen:

Hello, {} props.name
); } ; const element = ; ReactDOM.render (element, document.getElementById (’root’))

REACT element in this case is a ’use strict’; const element = React.createElement; greeting function () {return element (’h4’, null, ’Hello, world’!); } ; Depending on the application () {return element (greeting); } ; const domContainer = document.querySelector (’# root’); ReactDOM.render (element (App), domContainer);

This is a mocked, real-world example of what a functional ES5 component aspect is like when we are not using JSX, but plain JavaScript. Don’t worry too much about what’s going on in HTML. Put the focus on JavaScript logic - we have an item that is created, a function that returns something and this function is rendered in a kind of ReactDOM.

What is JSX -. short for JavaScript XML Extension - basically allows us to write HTML into our JavaScript in order to make it more like what we’re used to seeing in HTML. In the sample code above, we are simply using JavaScript to create our HTML element, then using React’s createElement method to insert a

in the DOM at

Functional components can be written ES5 or ES6. This is an example of what both an ES5 and ES6 functional component aspect like JSX use:

ES5 functional component

Functional component ES6

Prior to React v.16, functional components were known as stateless components. This means that the main purpose of the component should be presentation - to look good on the page. Quite often the data was passed to these functional components so that they could display something on the user interface.

With the advent of React v.16, everything changed. We’ll cover that in a bit. For now, you only need to know that there are functional components to receive some sort of data from a parent or global object to present something to the client.

Class Components

Class components are a bit more complicated than "just" a JavaScript function. Class components in React borrow the concept of the ES6 JavaScript class. The structure of a class in JavaScript is basically an object that has attributes and methods associated with it. We use the this keyword to access an instance of this object and to interact with it.

React, for the most part the structure is the same. . The components of the React class are an instance of an object and that object has what we call State at a high level, state is simply data that the component contains - just think of it as another way to define attributes and associate it with the class. As a developer, you can do whatever you want with this data: present it on the screen, pass it on to other components, use it to do other logic, etc.

Class component An ES6 is always uppercase, just like with functional components - it’s a React rule so the transpiler knows it’s a component. Since we are inheriting the component structure itself from React, we need to extend REACT Component. Within that block of code is where we’ll put our status:

{this.state.species.map (animal => {return })} )}} ReactDOM.render (, document.getElementById ( ’root’));

The state is an object full of properties and values. Our state has property here of all kinds, and its value is a host full of animals. For reference or to interact with this table, we use this.state.species.

The purpose of the component of the above class is to pass the name of the animal up to the component . component’s job is to do something with this data when it receives it. The state of the animal will be part of an accessory object when it is passed to a functional class or other component. It will be accessible in the child ’s components as long as it continues to be passed.

Just remember that in React, flows data from the parent component to the one-level child component. You have to move to another level if you need the data in the parent’s small- child component .

Another feature of class components in React is that we have access to methods and use lifecycle to keep track of our state. React lifecycles generally have three stages: they are created (Mount), live (Update ) and die (Unmount) There are access methods and / or state change at each of the stages of the lifecycle method:

  1. ComponentDidMount () - this is the lifecycle method where we make AJAX requests / network requests to initialize state. Use this.setState () to load data ées recovered to the state.
  2. ComponentDidUpdate () & ndash; status updates occur here after a user has interacted with the app.
  3. ComponentDidUnmount () - this is a cleanup function that occurs when the component is unmounted. It will take care of timers, AJAX requests, etc.

    There are more life cycle methods than these - the ones listed here are just the main ones. See the React documentation for more information on these methods.

    Finally, unlike the return declaration of functional components, class components use a render () method. This method is called after ReactDOM.render () passes the animal component and React calls its constructor. The state is then initialized and the rendering method is called to actually bring the content to the screen.

    Phew! That’s a lot of information.

    Just remember that functional components before React c. 16 are the most time the presentation - they do not reach the state - they do the show. The class components detailed all the state logic for us and passed the information to other components as accessories.

    Functional components and useState ()

    In 2018, React introduced the idea of ‚Äã‚Äã reaction hooks . The hooks are in a clear and concise manner using lifecycle and state processes in a functional component.

    Most of everything is very similar to anything we’ve covered so far. We have a state, we have to do something and we have to move to another place. The main goals are the same. The syntax is much clearer - you just need to get used to it.

    I would do is to bookmark this site, practice and get reps for class components, really understand how flow data in React and then return here to complete ’ learning about stateful functional components .

    Either let’s start with the code we had before:

    We have two or components, an animal and an application. App seems to come back animal and pass an object called name with a value of "Marshmallow".

    Believe it or not, there isn’t much we need to do to convert it to stateful logic. Let’s take a look at the component. We will take the following steps:

    - this line will import our hook, useState

    - this line initializes our state. State and setState are arbitrary words here. You can name them whatever you want. It is customary to name them after the value.

    - state is our actual state. The initial state is in parentheses in useState ().

    - setState is similar to this.setState (). This is the method that will change our state as we go through our application.

    - replace "Marshmallow" with {state}. When we need to write JSX JavaScript, we use braces. The braces here allow us to pass our variable.

    One of the defining characteristics of the class components, React’s lifecycle, with its various methods, is reduced to a basic hook that encapsulates all methods! The useEffect () hook can mount, update, and unmount the React component it is on.

    Conclusion

    Before React v. 16, the functional components were used exclusively as a presentation view layer without the use of state other than as props conveyed by the class components. Class components maintained all application state and transmitted data. The class components used lifecycle methods that mounted, updated , and unmounted our React component. We also found that React Hooks, a new model released by React in version 16, allows functional components to be stateful and have their own version of lifecycle methods.

    Just being important to know all the different types of components even React Hooks is becoming more and more popular - existing code will likely be using class components for some time and still need to be understood in order to be able to work there !

    Javascript Class Vs Function __del__: Questions

    How can I make a time delay in Python?

    5 answers

    I would like to know how to put a time delay in a Python script.

    2973

    Answer #1

    import time
    time.sleep(5)   # Delays for 5 seconds. You can also use a float value.
    

    Here is another example where something is run approximately once a minute:

    import time
    while True:
        print("This prints once a minute.")
        time.sleep(60) # Delay for 1 minute (60 seconds).
    

    2973

    Answer #2

    You can use the sleep() function in the time module. It can take a float argument for sub-second resolution.

    from time import sleep
    sleep(0.1) # Time in seconds
    

    How to delete a file or folder in Python?

    5 answers

    How do I delete a file or folder in Python?

    2639

    Answer #1


    Path objects from the Python 3.4+ pathlib module also expose these instance methods:

    Javascript Class Vs Function iat: Questions

    iat

    InsecurePlatformWarning: A true SSLContext object is not available. This prevents urllib3 from configuring SSL appropriately

    3 answers

    Tried to perform REST GET through python requests with the following code and I got error.

    Code snip:

    import requests
    header = {"Authorization": "Bearer..."}
    url = az_base_url + az_subscription_id + "/resourcegroups/Default-Networking/resources?" + az_api_version
    r = requests.get(url, headers=header)
    

    Error:

    /usr/local/lib/python2.7/dist-packages/requests/packages/urllib3/util/ssl_.py:79: 
              InsecurePlatformWarning: A true SSLContext object is not available. 
              This prevents urllib3 from configuring SSL appropriately and may cause certain SSL connections to fail. 
              For more information, see https://urllib3.readthedocs.org/en/latest/security.html#insecureplatformwarning.
      InsecurePlatformWarning
    

    My python version is 2.7.3. I tried to install urllib3 and requests[security] as some other thread suggests, I still got the same error.

    Wonder if anyone can provide some tips?

    334

    Answer #1

    The docs give a fair indicator of what"s required., however requests allow us to skip a few steps:

    You only need to install the security package extras (thanks @admdrew for pointing it out)

    $ pip install requests[security]
    

    or, install them directly:

    $ pip install pyopenssl ndg-httpsclient pyasn1
    

    Requests will then automatically inject pyopenssl into urllib3


    If you"re on ubuntu, you may run into trouble installing pyopenssl, you"ll need these dependencies:

    $ apt-get install libffi-dev libssl-dev
    

    iat

    Dynamic instantiation from string name of a class in dynamically imported module?

    3 answers

    In python, I have to instantiate certain class, knowing its name in a string, but this class "lives" in a dynamically imported module. An example follows:

    loader-class script:

    import sys
    class loader:
      def __init__(self, module_name, class_name): # both args are strings
        try:
          __import__(module_name)
          modul = sys.modules[module_name]
          instance = modul.class_name() # obviously this doesn"t works, here is my main problem!
        except ImportError:
           # manage import error
    

    some-dynamically-loaded-module script:

    class myName:
      # etc...
    

    I use this arrangement to make any dynamically-loaded-module to be used by the loader-class following certain predefined behaviours in the dyn-loaded-modules...

    222

    Answer #1

    You can use getattr

    getattr(module, class_name)
    

    to access the class. More complete code:

    module = __import__(module_name)
    class_ = getattr(module, class_name)
    instance = class_()
    

    As mentioned below, we may use importlib

    import importlib
    module = importlib.import_module(module_name)
    class_ = getattr(module, class_name)
    instance = class_()
    

    iat

    How to get all of the immediate subdirectories in Python

    3 answers

    I"m trying to write a simple Python script that will copy a index.tpl to index.html in all of the subdirectories (with a few exceptions).

    I"m getting bogged down by trying to get the list of subdirectories.

    184

    Answer #1

    import os
    def get_immediate_subdirectories(a_dir):
        return [name for name in os.listdir(a_dir)
                if os.path.isdir(os.path.join(a_dir, name))]
    

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