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Java script项目一:计数器

一、成果展示

二、代码
html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Counter</title>

    <!-- styles -->
    <link rel="stylesheet" href="styles.css" />
  </head>
  <body>
    <main>
      <div class="container">
        <h1>Counter</h1>
        <span id = "value">0</span>
        <div class="button-container">
          <button class="btn decrease">decrease</button>
          <button class="btn set">reset</button>
          <button class="btn increase">increase</button>  <!--输入.button, 直接显示<div class="button"></div>-->>
        </div>
      </div>

    </main>

    <!-- javascript -->
    <script src="app.js"></script>
  </body>
</html>

Js代码

//set initial count
let count = 0;

//select value and buttons
const value = document.querySelector('#value')
const btns = document.querySelectorAll(".btn")

btns.forEach(function(btn){                       //这里有一个function
    btn.addEventListener('click',function(e){     //这里有一个function
        const styles = e.currentTarget.classList
        if(styles.contains('decrease')){
            count--;
        } else if(styles.contains('increase')){
            count++;
        } else{
            count = 0;
        }
        if(count>0){
            value.style.color = "green";
        }
        if(count<0){
            value.style.color = "red";
        }
        if(count==0){                          //这里是==
            value.style.color = "#222";
        }
        value.textContent = count;

    });
});

https://www.youtube.com/watch?v=3PHXvlpOkf4

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