如何在 JavaScript 中声明块作用域变量?

javascriptweb developmentobject oriented programming更新于 2025/8/21 4:28:17

要声明块作用域变量，我们使用 ES2015 中引入的关键字 let 和 const。

以下是在 JavaScript 中声明黑色作用域变量的代码 −

示例

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Document</title>
<style>
   body {
      font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
   }
   .result,.sample {
      font-size: 20px;
      font-weight: 500;
   }
</style>
</head>
<body>
<h1>Declaring block scoped variables</h1>
<div class="sample"></div>
<div style="color: green;" class="result"></div>
<button class="btn">点击此处</button>
<h3>Click on the above button to declare and display block scoped variables</h3>
<script>
   let resEle = document.querySelector(".result");
   let sampleEle = document.querySelector(".sample");{
      let a = 22;
      const b = 44;
      sampleEle.innerHTML = "let a = " + a + "<br>";
      sampleEle.innerHTML += "const b = " + b + "<br>";
   }
   document.querySelector(".Btn").addEventListener("click", () => {
      try {
         a + b;
      }
      catch (err) {
         resEle.innerHTML = "a+b = " + err;
      }
   });
</script>
</body>
</html>