5.7 Global对象

Posted 2020-10-21 caijw

5.7 Global对象
encodeURI encodeURIComponent decodeURI decodeURIComponent
用特殊的utf-8编码替换所有无效的字符，从而让浏览器能理解

var uri = "http://www.baidu.com/illegal value.html#start";
l(encodeURI(uri));//http://www.baidu.com/illegal value.html#start
l(encodeURIComponent(uri));//http%3A%2F%2Fwww.baidu.com%2Fillegal%20value.html%23start
l(decodeURI(uri));//http://www.baidu.com/illegal value.html#start
l(decodeURIComponent(uri));//http://www.baidu.com/illegal value.html#start

eval 像一个完整的ECMAScript解析器
严格模式下可能，外部访问不了eval中创建的任何变量和参数

Gobal对象的属性

undefined NaN Infinity Object Array Function Boolean String Number
Date RegExp Error EvalError RangeError ReferenceError SyntaxError TypeError URIError

window 对象
在全局作用域中声明的所有变量和函数，都变成了window对象属性

var color = "red";
function sayColor(){
    l(window.color);
}
window.sayColor();//red

var global = function(){
    return this;
}

1. Math 对象的属性

   Math.e
   Math.LN10
   Math.LN2
   Math.LOG2E
   Math.LOG10e
   Math.PI
   Math.SQRT1_2
   Math.SQRT2

2. min max 方法

   var max = Math.max(3, 54, 32, 16);
   l(max);//54
   var min = Math.min(3, 54, 32, 16);
   l(min);//3
   //这个技巧的关键是把Math对象作为apply()的第一个参数，从而正确设置this
   var values = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
   var max = Math.max.apply(Math, values);
   l(max);//10

3. ceil floor round

   l(Math.ceil(25.9)); //26
   l(Math.ceil(25.5));// 26
   l(Math.ceil(25.1));// 26
   l(Math.floor(25.9));//25
   l(Math.floor(25.5));//25
   l(Math.floor(25.1));//25
   l(Math.round(25.9));//26
   l(Math.round(25.5));//26
   l(Math.round(25.1));//25

4. random 方法

   // 1-10
   var num = Math.floor(Math.random() * 10 +1);
   l(num);
   // 2-10
   var num = Math.floor(Math.random() * 9 + 2);
   l(num);
   // 随机函数
   function selectForm(lowerValue, upperValue){
   var choices = upperValue - lowerValue + 1;
   return Math.floor(Math.random()* choices + lowerValue);
   }
   var num = selectForm(2, 10);
   l(num);
   var colors = [‘red‘, ‘green‘, ‘blue‘, ‘yellow‘, ‘black‘, ‘purple‘, ‘brown‘];
   var color  = colors[selectForm(0, colors.length - 1)];
   l(color);

5. 其他方法
   Math.abs() Math.exp() Math.log() Math.pow() Math.sqrt() Math.acos()