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编辑您的代码：
<!DOCTYPE HTML> <html> <head> <script type="text/javascript"> function resCalc() { numA=document.getElementById("num_a").value; numB=document.getElementById("num_b").value; document.getElementById("result").value=Number(numA)+Number(numB); } </script> </head> <body> <p>使用 output 元素的简易计算器：</p> <form onsubmit="return false"> <input id="num_a" /> + <input id="num_b" /> = <output id="result" onforminput="resCalc()"></output> </form> </body> </html>
查看结果: