截取中间字符串
let str = "[img=http://123456]";
let imgUrl = str.match(/\[img=\S*\]/)[1];
console.log(imgUrl); //http://123456
let str = "[img=http://123456]";
let imgUrl = str.match(/\[img=\S*\]/)[1];
console.log(imgUrl); //http://123456