Tag: typescript

import React, {RefObject, useEffect} from "react";

function RefComponent() {

    const myRef: RefObject<HTMLParagraphElement> = React.createRef();

    useEffect(() => {
        console.log(myRef.current)
    });

    return (
        <p ref={myRef}>Hello World</p>
    );
}

export default RefComponent;

References
https://reactjs.org/docs/refs-and-the-dom.html

import React, {useState} from "react";

function Info() {
    const [name, setName] = useState("");

    return (
        <div>
            <div>
                <label>
                    Name:
                    <input type="text" placeholder="Enter your name" value={name}
                           onChange={event => {
                               setName(event.target.value)
                           }}/>
                </label>

            </div>
            <div>
                Result : Hello {name}
            </div>

        </div>
    );
}

export default Info;

In most cases, it’s recommend using controlled components to implement forms. In a controlled component, form data is handled by a React component. The alternative is uncontrolled components, where form data is handled by the DOM itself.

To write an uncontrolled component, instead of writing an event handler for every state update, you can use a ref to get form values from the DOM.

References
https://reactjs.org/docs/forms.html
https://reactjs.org/docs/uncontrolled-components.html
https://reactjs.org/docs/refs-and-the-dom.html

Counter.tsx

import {useState} from "react";

function Counter(props: CounterProp) {
    const [count, setCount] = useState(0)

    const buttonClicked = () => {
        setCount(prevState => {

            var result = prevState + 1;

            if (props.onCounterChanged != null) {
                props.onCounterChanged(result);
            }

            return result;
        })
    };

    return (
        <div>
            <div>Counter Value : {count}</div>
            <button className="bg-blue-500 hover:bg-blue-700 text-white font-bold py-2 px-4 rounded"
                    onClick={buttonClicked}>Next
            </button>
        </div>
    );
}

export interface CounterProp {
    onCounterChanged?: (value: number) => void;
}

export default Counter;

App.tsx

import React from 'react';
import Counter from "./components/Counter";

function App() {
    return (
        <div className={"px-1"}>
            <Counter onCounterChanged={(value => console.log(value))}></Counter>
        </div>

    );
}

export default App;

References
https://www.tutorialsteacher.com/typescript/typescript-interface
https://stackoverflow.com/questions/39713349/make-all-properties-within-a-typescript-interface-optional

import {useState} from "react";

function Counter() {
    const [count, setCount] = useState(0)

    const buttonClicked = () => {
        setCount(prevState => prevState + 1)
    };

    return (
        <div>
            <div>Counter Value : {count}</div>
            <button className="bg-blue-500 hover:bg-blue-700 text-white font-bold py-2 px-4 rounded"
                    onClick={buttonClicked}>Next
            </button>
        </div>
    );
}

export default Counter;

Passing Arguments to Event Handlers

import {useState} from "react";

function Counter() {
    const [count, setCount] = useState(0)

    const buttonClicked = (e: React.MouseEvent<HTMLButtonElement>) => {
        console.log(e);
        setCount(prevState => prevState + 1)
    };

    return (
        <div>
            <div>Counter Value : {count}</div>
            <button className="bg-blue-500 hover:bg-blue-700 text-white font-bold py-2 px-4 rounded"
                    onClick={(e) => buttonClicked(e)}>Next
            </button>
        </div>
    );
}

export default Counter;

Prevent default behavior

import {useState} from "react";

function Counter() {
    const [count, setCount] = useState(0)

    const buttonClicked = (e: React.MouseEvent<HTMLButtonElement>) => {
        if (e.cancelable)
        {
            e.preventDefault();
        }

        setCount(prevState => prevState + 1)
    };

    return (
        <div>
            <div>Counter Value : {count}</div>
            <button className="bg-blue-500 hover:bg-blue-700 text-white font-bold py-2 px-4 rounded"
                    onClick={(e) => buttonClicked(e)}>Next
            </button>
        </div>
    );
}

export default Counter;

The preventDefault() method cancels the event if it is cancelable, meaning that the default action that belongs to the event will not occur.

For example, this can be useful when:

• Clicking on a “Submit” button, prevent it from submitting a form
• Clicking on a link, prevent the link from following the URL

Note: Not all events are cancelable. Use the cancelable property to find out if an event is cancelable.

Note: The preventDefault() method does not prevent further propagation of an event through the DOM. Use the stopPropagation() method to handle this.

References
https://reactjs.org/docs/handling-events.html
https://www.w3schools.com/jsref/event_preventdefault.asp
https://stackoverflow.com/questions/32298064/preventdefault-not-working-in-on-input-function

Greeting.tsx

function Greeting(props:GreetingProps) {
    return (
        <p className="px-1 py-4 font-bold text-red-700">Hello {props.name}</p>
    );
}

export interface GreetingProps {
    name:string
}

export default Greeting;

App.tsx

import React from 'react';
import Greeting from "./components/Greeting";

function App() {
  return (
    <Greeting name={"Mahmood"}></Greeting>
  );
}

export default App;

References
https://reactjs.org/docs/components-and-props.html