import React.Component from 'react'
import [ Component ] from 'react'
import Component from 'react'
import { Component } from 'react'
React.memo
higher-order component.useReducer
Hook.useMemo
Hook.shouldComponentUpdate
lifecycle method.const person =(firstName, lastName) =>
{
first: firstName,
last: lastName
}
console.log(person("Jill", "Wilson"))
import React, {useState} from 'react';
const name = 'Rachel';
const age = 31;
const person = { name, age };
console.log(person);
{name: "Rachel", age: 31}
{person: "Rachel", person: 31}}
{person: {name: "Rachel", age: 31}}
const topics = ['cooking', 'art', 'history'];
const first = ["cooking", "art", "history"]
const [] = ["cooking", "art", "history"]
const [, first]["cooking", "art", "history"]
const [first] = ["cooking", "art", "history"]
const [, , animal] = ['Horse', 'Mouse', 'Cat'];
console.log(animal);
<Message {...props} />
<Route path="/:id" />
function Dish() {
return <h1>Mac and Cheese</h1>;
}
ReactDOM.render(<Dish />, document.getElementById('root'));
div
h1
React.createElement('h1', null, "What's happening?");
<h1 props={null}>What's happening?</h1>
<h1>What's happening?</h1>
<h1 id="component">What's happening?</h1>
<h1 id="element">What's happening?</h1>
function MyComponent() {
return (
<Suspense>
<div>
<Message />
</div>
</Suspense>
);
}
const message = 'Hi there';
const element = <p>{message}</p>;
React.memo
React.split
React.lazy
React.fallback
useLayoutEffect
?A. <button onClick={this.handleClick}>Click Me</button>
B. <button onClick={event => this.handleClick(event)}>Click Me</button>
function Dish(props) {
return (
<h1>
{props.name} {props.cookingTime}
</h1>
);
}
function Dish([name, cookingTime]) { return <h1>{name} {cookingTime}</h1>; }
function Dish({name, cookingTime}) { return <h1>{name} {cookingTime}</h1>; }
function Dish(props) { return <h1>{name} {cookingTime}</h1>; }
function Dish(...props) { return <h1>{name} {cookingTime}</h1>; }
React.PureComponent
?shouldComponentUpdate()
getDerivedStateFromProps()
is an unsafe method to useconst Heading = () => {
<h1>Hello!</h1>;
};
h1
tag.h1
to another component.h1
in a div
.**__**
with respect to their props.[e.target.id]
called in the following code snippet?handleChange(e) {
this.setState({ [e.target.id]: e.target.value })
}
class Clock extends React.Component {
render() {
return <h1>Look at the time: {time}</h1>;
}
}
Array.map()
function?setState
instead of an object?setState
is asynchronous and might result in out of sync values.React
ReactDOM
Render
DOM
value
property.defaultValue
property.default
property.class clock extends React.Component {
render() {
return <h1>Look at the time: {this.props.time}</h1>;
}
}
this
clock
useEffect(function updateTitle() { document.title = name + ' ' + lastname; });
useEffect(() => { title = name + ' ' + lastname; });
useEffect(function updateTitle() { name + ' ' + lastname; });
useEffect(function updateTitle() { title = name + ' ' + lastname; });
React.fallback
React.split
React.lazy
React.memo
function MyComponent(props) {
const [done, setDone] = useState(false);
return <h1>Done: {done}</h1>;
}
useEffect(() => { setDone(true); });
useEffect(() => { setDone(true); }, []);
useEffect(() => { setDone(true); }, [setDone]);
useEffect(() => { setDone(true); }, [done, setDone]);
class Huggable extends React.Component {
hug(id) {
console.log("hugging " + id);
}
render() {
let name = "kitteh";
let button = // Missing Code
return button;
}
}
<button onClick={(name) => this.hug(name)>Hug Button</button>
<button onClick={this.hug(e, name)}>Hug Button</button>
<button onClick={(e) => hug(e, name)}>Hug Button</button>
<button onClick={(e) => this.hug(name, e)}>Hug Button</button>
handleClick
is being called instead of passed as a reference. How do you fix this?<button onClick={this.handleClick()}>Click this</button>
<button onClick={this.handleClick.bind(handleClick)}>Click this</button>
<button onClick={handleClick()}>Click this</button>
<button onClick={this.handleClick}>Click this</button>
<button onclick={this.handleClick}>Click this</button>
fetch()
function come from?fetch()
is supported by most browsers.useEffect(() => {
setName('John');
}, [name]);
this.setState(...)
this.forceUpdate()
class Button extends React.Component{
constructor(props) {
super(props);
// Missing line
}
handleClick() {...}
}
this.handleClick.bind(this);
props.bind(handleClick);
this.handleClick.bind();
this.handleClick = this.handleClick.bind(this);
<React.Fragment>
<h1>Our Staff</h1>
<p>Our staff is available 9-5 to answer your questions</p>
</React.Fragment>
<...>
<h1>Our Staff</h1>
<p>Our staff is available 9-5 to answer your questions</p>
</...>
<//>
<h1>Our Staff</h1>
<p>Our staff is available 9-5 to answer your questions</p>
<///>
<>
<h1>Our Staff</h1>
<p>Our staff is available 9-5 to answer your questions</p>
</>
<Frag>
<h1>Our Staff</h1>
<p>Our staff is available 9-5 to answer your questions</p>
</Frag>
h1
?class Ticker extends React.component {
constructor(props) {
super(props);
this.state = { count: 0 };
}
render() {
return <h1>{}</h1>;
}
}
const greeting = isLoggedIn ? <Hello /> : null;
isLoggedIn
is trueReactDOM.render(<Message orderNumber="16" />, document.getElementById('root'));
h1
but there is an unexpected token error when it runs. How do you fix this?const element = <h1 style={ backgroundColor: "blue" }>Hi</h1>;
const element = <h1 style="backgroundColor: "blue""}>Hi</h1>;
const element = <h1 style=>Hi</h1>;
const element = <h1 style={blue}>Hi</h1>;
const element = <h1 style="blue">Hi</h1>;
replaceState
refreshState
updateState
setState
const Star = ({ selected = false }) => <Icon color={selected ? 'red' : 'grey'} />;
A function component is the same as a class component.
A function component accepts a single props object and returns a React element.
A function component is the only way to create a component.
A function component is required to create a React component.
FetchJS
ReactDOM
No library. fetch() is supported by most browsers.
React
A. <button onClick=fthis.handleClickl>Click Me</button>
B. <button onClick={event => this.handleClick(event)}>Click Me</button>
Button A will not have access to the event object on click of the button
Button A will not fire the handler this.handleClick successfully
There is no difference
Button B will not fire the handler this.handleClick successfully
useEffect(() => {
setName('John');
}, [name]);
It will cause an error immediately.
It will execute the code inside the function, but only after waiting to ensure that no other component is accessing the name variable.
It will update the value of name once and not run again until name is changed from the outside.
It will cause an infinite loop.
<Route path="/:id" />
javascript <Route path="/:id"> <About /> </Route> ```
javascript <Route path="/tid" about={Component} /> ```
javascript <Route path="/:id" route={About} /> ```
javascript <Route> <About path="/:id" /> </Route> ```
const Greeting ({ name }) > <h1>Hello {name}!</h1>;
javascript class Greeting extends React.Component { constructor() { return <h1>Hello (this.props.name)!</h1>; } } ```
javascript class Greeting extends React.Component { <h1>Hello (this.props.name}!</h1>; } ```
javascript class Greeting extends React.Component { return <h1>Hello (this.props.name) 1</h1>; } ```
javascript class Greeting extends React.Component ( render({ name }) { return <h1>Hello (name)} !</h1>; }) ```
ReactDOM.render(
<h1>Hi<h1>,
document.getElementById('root')
)
<a>
tag in React?Back
button.Link
component is just another name for the <a>
tag.<a>
tag will cause an error when used in React.<a>
tag triggers a full page reload, while the Link
component does not.x
, that is sent to the createElement
function?React.createElement(x, y, z);
useEffect(() => {
// do things
}, []);
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