Run-time errors arise from design faults, coding mistakes, hardware failures, and many other sources. Although you cannot anticipate all possible errors, you can plan to handle certain kinds of errors meaningful to your PL/SQL program.
When you want a component to “remember” some information, but you don’t want that information to trigger new renders, you can use a ref.
import { useRef } from 'react';
let ref = useRef(0);
{
current: 0 // The value you passed to useRef
}
- Refs are an escape hatch to hold onto values that aren’t used for rendering. You won’t need them often.
- A ref is a plain JavaScript object with a single property called current, which you can read or set.
- You can ask React to give you a ref by calling the useRef Hook.
- Like state, refs let you retain information between re-renders of a component.
- Unlike state, setting the ref’s current value does not trigger a re-render.
- Don’t read or write ref.current during rendering. This makes your component hard to predict.
References
ALL_DIRECTORIES (OWNER, DIRECTORY_NAME, DIRECTORY_PATH)
This view describes all directories accessible to the user.
SELECT * FROM ALL_DIRECTORIES;
DBA_DIRECTORIES(OWNER, DIRECTORY_NAME, DIRECTORY_PATH)
This view describes all directories specified for the entire database.
SELECT * FROM DBA_DIRECTORIES;
References
In CSS modules, CSS class names and animation names are scoped locally by default. In React you can use the file naming conversion as [file name].module.css. This let the React and Webpack know that you are using CSS Modules.
Importing the CSS in the file.
import nameyoulike from './name.modules.css';
Calling the style in the file.
<button className={styles.button} />
References
Styled-components is a CSS-in-JS library that enables you to write regular CSS and attach it to JavaScript components. With styled-components, you can use the CSS you’re already familiar with instead of having to learn a new styling structure.
Utilising tagged template literals (a recent addition to JavaScript) and the power of CSS, styled-components allows you to write actual CSS code to style your components.
References
React and ReactDOM are two separate libraries that are often used together in the development of web applications with React.
React is a JavaScript library for building user interfaces. It is designed to be declarative, meaning that developers specify what the UI should look like based on the current state of the application, and React takes care of updating the UI as needed. React is designed to be efficient and flexible, and is widely used in the development of web and mobile applications.
ReactDOM, on the other hand, is a library that provides an interface between React and the DOM (Document Object Model). The DOM is a tree-like structure that represents the HTML of a web page, and ReactDOM provides a set of functions that allow React components to be rendered to the DOM and updated efficiently.
In short, React is a library for building user interfaces, while ReactDOM is a library for interacting with the DOM and rendering React components to the web page. While they are often used together, they serve different purposes and can be used independently of each other.
Your components will often need to display different things depending on different conditions. In React, you can conditionally render JSX using JavaScript syntax like if statements, &&, and ? : operators.
References
Lifting state up in react means moving data from a child component to some parent component either to use it there or pass it some other child component.
- When you want to coordinate two components, move their state to their common parent.
- Then pass the information down through props from their common parent.
- Finally, pass the event handlers down so that the children can change the parent’s state.
- It’s useful to consider components as “controlled” (driven by props) or “uncontrolled” (driven by state).
It is common to call a component with some local state “uncontrolled”.
In contrast, you might say a component is “controlled” when the important information in it is driven by props rather than its own local state. This lets the parent component fully specify its behavior.
When writing a component, consider which information in it should be controlled (via props), and which information should be uncontrolled (via state). But you can always change your mind and refactor later.
References
There are many default browser actions:
mousedown– starts the selection (move the mouse to select).clickon<input type="checkbox">– checks/unchecks the input.submit– clicking an<input type="submit">or hitting Enter inside a form field causes this event to happen, and the browser submits the form after it.keydown– pressing a key may lead to adding a character into a field, or other actions.contextmenu– the event happens on a right-click, the action is to show the browser context menu.- …there are more…
All the default actions can be prevented if we want to handle the event exclusively by JavaScript.
To prevent a default action – use either event.preventDefault() or return false. The second method works only for handlers assigned with on<event>.
The passive: true option of addEventListener tells the browser that the action is not going to be prevented. That’s useful for some mobile events, like touchstart and touchmove, to tell the browser that it should not wait for all handlers to finish before scrolling.
If the default action was prevented, the value of event.defaultPrevented becomes true, otherwise it’s false.