摘要：趙錢孫李截取從第二位之后的三位趙錢孫李趙錢孫李趙錢孫李趙錢孫李內置對象返回指定字符串的位置沒找到沒找到字符串拼接一般用類的靜態方法不需要需要的是對象方法四舍五入瀏覽器對象的重要性不聲明污染全局

  // for 
  var arr = ["趙", "錢", "孫", "李"];
  for (var i = 0; i < arr.length; i++) {
    console.log(arr[i]);
  }
  var obj = { name: "list", age: 26, area: "bj" };
  for (var j in obj) {
    console.log(j + " ~ " + obj[j]);
  }
  
  
  // obj 
  var str = "hello world";
  console.log(str);// hello world
  console.log(str.length);// 11
  console.log(str.substr(2, 3));// llo截取從第二位之后的三位
  console.log(str.split());// ["hello world"]
  console.log(str.split(""));// ["h", "e", "l", "l", "o", " ", "w", "o", "r", "l", "d"]
  console.log(str.split(" "));// ["hello", "world"]
  var arr = ["趙", "錢", "孫", "李"];
  console.log(arr.join());// 趙,錢,孫,李
  console.log(arr.join(""));// 趙錢孫李
  console.log(arr.join("-"));// 趙-錢-孫-李
  
  
  
  // js內置對象
  // str
  var str = "helloworld";
  console.log(str.indexOf("he"));// 0 返回指定字符串的位置
  console.log(str.indexOf("a"));// -1 沒找到
  console.log(str.length);// -1 沒找到
  console.log(str.concat("!"));// 字符串拼接
  console.log(str.replace("ll", "LL"));// heLLoworld
  console.log(str.toUpperCase());//   HELLOWORLD
  console.log(str.toUpperCase().toLowerCase());// helloworld
  // Date
  var dt = new Date();
  console.log(dt.getYear());// 一般用getFullYear
  console.log(dt.getFullYear()); // xxxx
  console.log(dt.getMonth());// 0-11
  console.log(dt.getDate());// 1-31 the day of the month
  console.log(dt.getDay());// 0-6 the day of the week
  console.log(dt.getHours());// 0-23
  console.log(dt.getMinutes());// 0-59
  console.log(dt.getSeconds());// 0-59
  console.log(dt.getMilliseconds());// 0-999
  // Math 類的靜態方法 不需要new 需要new的是對象方法
  console.log(Math.random());// [0, 1)
  console.log(Math.random() * 5 + 5);// [5, 10)
  console.log(Math.ceil("2.6"));// 3
  console.log(Math.floor("2.6"));// 2 
  console.log(Math.round("2.6"));// 3 四舍五入
  console.log(Math.sqrt(3 * 3));// 3
  console.log(Math.min(1, 2));// 1
  console.log(Math.max(1, 2));// 2
  console.log(Math.pow(7, 2));// 7*7
  // arr 
  var arr = [];
  conlsole.log(arr.length);// 
  conlsole.log(arr.concat());// 
  conlsole.log(arr.join());// 
  conlsole.log(arr.pop());// 
  conlsole.log(arr.push());// 
  conlsole.log(arr.shift());// 
  conlsole.log(arr.unshift());// 
  conlsole.log(arr.sort());// 
  conlsole.log(arr.reverse());// 
  conlsole.log(arr.slice);// charu
  conlsole.log(arr.splice());// del
  
  
  
  // 瀏覽器window對象
  // window.alert();
  // window.confirm();
  console.log(window.navigator);
  console.log(window.navigator.cookieEnabled);
  console.log(window.location);
  console.log(window.location.search);// ?id=2
  console.log(window.history);
  // console.log(window.history.forward());
  // console.log(window.history.go());
  console.log(window.screen);
  console.log(window.screen.width);
  console.log(window.screen.availHeight);
  console.log(window.document);
  
  
  
  
  // var的重要性 不聲明污染全局union
  window.str = "union";
  function t1() {
    var str = "china";
    function t2() {
      var str = "japan";
      // alert(str);
    }
    t2();
  }
  t1();