react课程4-compoment

这次课程创建了一个小组件，

下载了dev tools

一、代码

（1）App.js

import { useState } from "react";

const messages = [
  "Learn React ⚛️",
  "Apply for jobs 💼",
  "Invest your new income 🤑",
];

export default function App() {
  const [step, setStep] = useState(1);
  const [isOpen, setIsOpen] = useState(true);

  function handlePrevious() {
    if (step > 1) setStep((s) => s - 1);
  }

  function handleNext() {
    if (step < 3) setStep((s) => s + 1);
  }

  return (
    <>
      <button className="close" onClick={() => setIsOpen((is) => !is)}>
        &times;
      </button>
      {isOpen && (
        <div className="steps">
          <div className="numbers">
            <div className={`${step >= 1 ? "active" : ""}`}>1</div>
            <div className={`${step >= 2 ? "active" : ""}`}>2</div>
            <div className={`${step === 3 ? "active" : ""}`}>3</div>
          </div>

          <StepMessage step={step}>{messages[step - 1]}</StepMessage>

          <div className="buttons">
            <Button bgColor="#7950f2" textColor="#fff" onClick={handlePrevious}>
              <span>👈</span>Previous
            </Button>
            <Button bgColor="#7950f2" textColor="#fff" onClick={handleNext}>
              Next<span>👉</span>
            </Button>
          </div>
        </div>
      )}
    </>
  );
}

function StepMessage({ step, children }) {
  return (
    <div className="message">
      <h3>Step {step}</h3>
      {children}
    </div>
  );
}

function Button({ textColor, bgColor, onClick, children }) {
  return (
    <button
      style={{ backgroundColor: bgColor, color: textColor }}
      onClick={onClick}
    >
      {children}
    </button>
  );
}

（2）index.css

* {
  box-sizing: border-box;
}

body {
  font-family: sans-serif;
  color: #333;
}

.steps {
  width: 600px;
  background-color: #f7f7f7;
  border-radius: 7px;
  padding: 25px 100px;
  margin: 100px auto;
}

.numbers {
  display: flex;
  justify-content: space-between;
}

.numbers > div {
  height: 40px;
  aspect-ratio: 1;
  background-color: #e7e7e7;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 18px;
}

.numbers .active {
  background-color: #7950f2;
  color: #fff;
}

.message {
  text-align: center;
  font-size: 20px;
  margin: 40px 0;
  font-weight: bold;

  display: flex;
  flex-direction: column;
  align-items: center;
}

.buttons {
  display: flex;
  justify-content: space-between;
}

.buttons button {
  border: none;
  cursor: pointer;
  padding: 10px 15px;
  border-radius: 100px;
  font-size: 14px;
  font-weight: bold;

  display: flex;
  align-items: center;
  gap: 10px;
}

.buttons button span {
  font-size: 16px;
  line-height: 1;
}

h3 {
  margin: 0;
  text-transform: uppercase;
}

.close {
  position: absolute;
  top: 16px;
  right: 16px;
  border: none;
  background: none;
  cursor: pointer;
  font-size: 40px;
  color: inherit;
}

.close:hover {
  color: #7950f2;
}

二、重点回顾

状态的应用（非常之重要）

回调函数

html表单：onSubmit（按下Enter键也可以提交）与onClick监听事件的不同

受控元素

onClick（）监控

状态提升（到最近公共祖先）

重用组件、children传递