识别 JavaScript 中的 False 值

javascriptweb developmentobject oriented programming更新于 2025/9/4 19:56:17

JavaScript 中以下值在作为布尔类型 − 求值时会求值为 false false

0
空字符串:""" 、'' 或 ``
null
undefined
NaN - 不是数字值

以下是识别 JavaScript 中假值的代码 −

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{
      font-size: 20px;
      font-weight: 500;
      color: blueviolet;
   }
</style>
</head>
<body>
<h1>Identifying Falsy values in JavaScript.</h1>
<div class="result"></div>
<br />
<button class="btn">点击此处</button>
<h3>Click on the above button to identify some of the falsy values in JavaScript</h3>
<script>
   let resEle = document.querySelector(".result");
   let BtnEle = document.querySelector(".Btn");
   BtnEle.addEventListener("click", () => {
      if(!0){
         resEle.innerHTML = '0 evaluates to boolean false <br>';
      }
      if(!''){
         resEle.innerHTML += " '' evaluates to boolean false <br>";
      }
      if(!null){
         resEle.innerHTML += 'null evaluates to boolean false <br>';
      }
      if(!undefined){
         resEle.innerHTML += 'undefined evaluates to boolean false <br>';
      }
      if(!NaN){
         resEle.innerHTML += 'Nan evaluates to boolean false <br>';
      }
   });
</script>
</body>
</html>