console 命令行工具 X clear

console

window.onload = function() {
  var aInput = document.getElementsByTagName('input');
	<!-- var val = aInput[0].value;  (代码错误放置位置) 分析结果会怎样-->  
  aInput[1].onclick = function() {
    var val = aInput[0].value;
    if (detectNume(val)) {
      alert('is a Num');
    } else {
      alert('Not a num')
    }
  }

  function detectNume(str) {
    n = 0;
    for (var i = 0; i < str.length; i++) {
      n = str.charCodeAt(i);
      if (n < 48 || n > 57) return false;
    }
    return true;
  }

}

<!DOCTYPE html>
<html lang="en">
  
  <head>
    <meta charset="UTF-8" />
    <title>
      Document
    </title>
  </head>
  
  <body>
    <input type="text" />
    <input type="button" value='检测' />
  </body>

</html>