React list rendering
In real development, we will request a large amount of data from the server, and the data will be stored in the form of a list:
Data such as songs, artists, and chart lists;
Such as product, shopping cart, review list data;
Such as friend messages, news, contact list data;
In React, there is no v-for directive like the Vue module syntax, and we need to organize data through JavaScript code and convert it into JSX :
Many small partners who have transformed from Vue to React are very unaccustomed, and think that the way of Vue is more concise and clear;
But JSX in React is more flexible because of its seamless connection with JavaScript;
Also I often mention React as a way to really improve our ability to write code;
How to display the list?
In React, the most common way to display lists is to use arrays
map高阶函数;
class App extends React.Component {
constructor() {
super()
this.state = {
students: [
{
name: "aaa", age: 18, score: 99, id: 101},
{
name: "bbb", age: 19, score: 88, id: 102},
{
name: "ccc", age: 17, score: 77, id: 103},
{
name: "ddd", age: 17, score: 98, id: 104}
]
}
}
render() {
const {
students } = this.state
return (
<div>
{
students.map(stu => {
return(
<div key={
stu.id}>
<h3>学号: {
stu.name}</h3>
<h3>年龄: {
stu.age}</h3>
<h3>成绩: {
stu.score}</h3>
</div>
)
})
}
</div>
)
}
}
const app = ReactDOM.createRoot(document.querySelector("#app"))
app.render(<App/>)
Many times before we display the data in an array, we need to do some processing on it :
For example, to filter out some content: filter function; for example, in the above code, it is required to display students whose scores are greater than 80
class App extends React.Component {
constructor() {
super()
this.state = {
students: [
{
name: "aaa", age: 18, score: 99, id: 101},
{
name: "bbb", age: 19, score: 88, id: 102},
{
name: "ccc", age: 17, score: 77, id: 103},
{
name: "ddd", age: 17, score: 98, id: 104}
]
}
}
render() {
const {
students } = this.state
// 对数组过滤再遍历
const filterStudents = students.filter(item => {
return item.score > 80
})
return (
<div>
{
filterStudents.map(stu => {
return(
<div key={
stu.id}>
<h3>学号: {
stu.name}</h3>
<h3>年龄: {
stu.age}</h3>
<h3>成绩: {
stu.score}</h3>
</div>
)
})
}
</div>
)
}
}
const app = ReactDOM.createRoot(document.querySelector("#app"))
app.render(<App/>)
For example, to intercept a part of the array: slice function, for example, in the above code, it is required to intercept the first two items of the array for display
class App extends React.Component {
constructor() {
super()
this.state = {
students: [
{
name: "aaa", age: 18, score: 99, id: 101},
{
name: "bbb", age: 19, score: 88, id: 102},
{
name: "ccc", age: 17, score: 77, id: 103},
{
name: "ddd", age: 17, score: 98, id: 104}
]
}
}
render() {
const {
students } = this.state
// 对数组截取再遍历
const spliceStudents = students.splice(0,2)
return (
<div>
{
spliceStudents.map(stu => {
return(
<div key={
stu.id}>
<h3>学号: {
stu.name}</h3>
<h3>年龄: {
stu.age}</h3>
<h3>成绩: {
stu.score}</h3>
</div>
)
})
}
</div>
)
}
}
const app = ReactDOM.createRoot(document.querySelector("#app"))
app.render(<App/>)
The above operation is filtered first, then intercepted, and finally traversed. In fact, it can be completed by chaining a line of code.
class App extends React.Component {
constructor() {
super()
this.state = {
students: [
{
name: "aaa", age: 18, score: 99, id: 101},
{
name: "bbb", age: 19, score: 88, id: 102},
{
name: "ccc", age: 17, score: 77, id: 103},
{
name: "ccc", age: 17, score: 77, id: 103},
{
name: "ddd", age: 17, score: 98, id: 104}
]
}
}
render() {
const {
students } = this.state
return (
<div>
{
/* 链式调用, 一步操作完成 */}
{
students.filter(item => item.score > 80).splice(0, 2).map(stu => {
return(
<div key={
stu.id}>
<h3>学号: {
stu.name}</h3>
<h3>年龄: {
stu.age}</h3>
<h3>成绩: {
stu.score}</h3>
</div>
)
})
}
</div>
)
}
}
const app = ReactDOM.createRoot(document.querySelector("#app"))
app.render(<App/>)
We will find that if there is no key binding in the previous code, a warning will be reported. This warning tells us that we need to add a key to the jsx displayed in the list
The main function of the key is to improve the efficiency of the diff algorithm;