JS中正则表达式要注意lastIndex属性

var reg = /JavaScript/;
reg.source; //返回 JavaScript

var str = "JavaScript";
str.match(/JavaScript/); //只能匹配一个JavaScript 
var str = "JavaScript JavaScript";
str.match(/JavaScript/g); //能匹配两个JavaScript 
var reg = /JavaScript/;
reg.global; //返回 false
var reg = /JavaScript/g;
reg.global; //返回 true

var reg = /JavaScript/;
reg.ignoreCase; //返回 false
var reg = /JavaScript/i;
reg.ignoreCase; //返回 true
var reg = /JavaScript/;
reg.test("javascript"); //返回 false
var reg = /JavaScript/i;
reg.test("javascript"); //返回 true

var str="java\nJavaScript";
str.match(/^JavaScript/); //返回null
var str="java\nJavaScript";
str.match(/^JavaScript/m); //匹配到一个JavaScript
var reg=/JavaScript/;
reg.multiline; //返回false
var reg=/JavaScript/m;
reg.multiline; //返回true

var str="java";
var reg=/JavaScript/;
reg.test(str); //返回false
var str="JavaScript";
var reg=/JavaScript/;
reg.test(str); //返回true

var str="JavaScript";
var reg=/JavaScript/g;
console.log(reg.test(str)); //打印 true
console.log(reg.test(str)); //打印 false

var str="JavaScript";
var reg=/JavaScript/g;
console.log(reg.test(str)); //打印 true
console.log(reg.lastIndex);
//打印10，因为匹配到了JavaScript，所以设置lastIndex为匹配结果紧挨着的字符位置
console.log(reg.test(str));
//打印 false，因为从lastIndex位置检索字符串，已经没有匹配结果了
console.log(reg.lastIndex);
//打印0，因为没有匹配到结果，所以将lastIndex重置为0

var str="java JavaScript java";
var reg=/JavaScript/g;
console.log(reg.test(str)); //打印 true
reg.lastIndex=0;
console.log(reg.test(str)); //打印 true