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<!DOCTYPE html> <html> <body> <h2>JavaScript</h2> <p>如果将值设置为 <b>undefined</b>，则可以清空变量。</p> <p id="demo"></p> <script> var car = "Volvo"; car = undefined; document.getElementById("demo").innerHTML = car + "<br>" + typeof car; </script> </body> </html>