JavaScript reference data type single built-in object

JavaScript reference data type single built-in object

1. Global object

1-1. Encoding

var uri = 'http://www,worx.com/illegal value.htm#start';

console.log(encodeURI(uri));       //http://www,worx.com/illegal%20value.htm#start

//整个URI进行编码，以便发送给浏览器，encodeURI不会对本身属于URI的特殊符号进行编码，只有空格被替换成%20

console.log(encodeURIComponent(uri));  //http%3A%2F%2Fwww%2Cworx.com%2Fillegal%20value.htm%23start

//用于对URI的某一段进行编码,encodeURIComponent会对它发现的任何非标准字符进行编码，使用对应的编码替换所有非字母数字字符

1-2. Decoding

var uri = 'http%3A%2F%2Fwww%2Cworx.com%2Fillegal%20value.htm%23start'

console.log(decodeURIComponent(uri));//只能对encodeURIComponent替换的字符进行解码

console.log(decodeURI(uri));//只会对%20解码为空格  //只能对encodeURI替换的字符进行解码

1-3. eval() method ECMAscript parser

eval("console.log('hi')");//<==>console.log('hi')

eval('function sayhi(){console.log("hello");}')//在eval()中创建的任何变量或函数都不会被提升，它们只在eval()执行时被创建

sayhi()

var global = function(){
    
    
  return this;
}();
console.log(global);

2. Math object

2-1、Math.max()、Math.min()

var max = Math.max(3,12,43,12);

console.log(max);//43

var min = Math.min(3,12,43,12);

console.log(min);//3

var values = [1,2,3,4,5]

var max = Math.max.apply(Math,values);

console.log(max);//5

2-2. Rounding method

(1) Perform upward rounding

console.log(Math.ceil(25.9));//26

console.log(Math.ceil(25.5));//26

console.log(Math.ceil(25.2));//26

(2) Perform standard rounding

console.log(Math.round(25.9));//26

console.log(Math.round(25.5));//26

console.log(Math.round(25.2));//25

(3) Perform downward rounding

console.log(Math.floor(25.9));//25

console.log(Math.floor(25.5));//25

console.log(Math.floor(25.2));//25

2-3. random() returns a number greater than 0 and less than 1

var num = Math.floor(Math.random()*10+1)

console.log(num);

function selectFrom(lower,upper){
    
    

  var choice = upper - lower + 1;

  return Math.floor(Math.random()*choice + lower);

}

var num = selectFrom(2,10);//随机生成2到10之间的随机数

console.log(num);

"Advanced Programming with Javascript" (3rd Edition) Chapter 5 - Notes