<!DOCTYPE html> <html> <body> <h1>JavaScript typeof</h1> <p>typeof 运算符返回变量或表达式的类型。</p> <p id="demo"></p> <script> document.getElementById("demo").innerHTML = typeof "john" + "<br>" + typeof 3.14 + "<br>" + typeof true + "<br>" + typeof false + "<br>" + typeof x; </script> </body> </html>