y18学习笔记1

摘要：赵钱孙李截取从第二位之后的三位赵钱孙李赵钱孙李赵钱孙李赵钱孙李内置对象返回指定字符串的位置没找到没找到字符串拼接一般用类的静态方法不需要需要的是对象方法四舍五入浏览器对象的重要性不声明污染全局

</>复制代码 
  // for 
  var arr = ["赵", "钱", "孙", "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截取从第二位之后的三位
  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 = ["赵", "钱", "孙", "李"];
  console.log(arr.join());// 赵,钱,孙,李
  console.log(arr.join(""));// 赵钱孙李
  console.log(arr.join("-"));// 赵-钱-孙-李
  
  
  
  // js内置对象
  // 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 没找到
  console.log(str.length);// -1 没找到
  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 类的静态方法 不需要new 需要new的是对象方法
  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
  
  
  
  // 浏览器window对象
  // 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 不声明污染全局union
  window.str = "union";
  function t1() {
    var str = "china";
    function t2() {
      var str = "japan";
      // alert(str);
    }
    t2();
  }
  t1();