js解析富文本符号，网上找了一下教程，大概都是这样写的：
str = str.replace(/∀/g, '∀');
str = str.replace(/∂/g, '∂');
str = str.replace(/&exists;/g, '∃');
str = str.replace(/∅/g, '∅');
str = str.replace(/∇/g, '∇');
str = str.replace(/∈/g, '∈');
只需转换常用的特殊符号的话，这样写似乎没什么问题。但是我百度到一个有700多个特殊符号的对照表（有首字母大写小写两种的，找不到相关链接了）。把700多个替换语句写在同一个函数里，微信小程序编译的时候会报错：
Error:file:
component/WxParse/wxParse/wxDiscode.js Maximum call stack size exceeded
所以显然不能每个符号调用一次替换是不科学的。代替的方法是改成用replace的回调函数。
var SupplementCode = [{c:"↖",e:"↖"},{c:"↗","e":"↗"},{c:"↘","e":"↘"},{c:"↙","e":"↙"},{c:"©","e":"©"},{c:"®","e":"®"},{c:"@","e":"@"},{c:"✓","e":"✓"},{c:"$","e":"$"},{c:"¢","e":"¢"},{c:"£","e":"£"},{c:"¥","e":"¥"},{c:"+","e":"+"},{c:"×","e":"×"}];
var SupplementCodeMatch = `(↖)|(↗)|(↘)|(↙)|(©)|(®)|(@)|(✓)|($)|(¢)|(£)|(¥)|(+)|(×)`;
var str = str.replace(new RegExp(SupplementCodeMatch,'ig'), function(s){
let entry = SupplementCode.find(a=>a.c==s);
return entry?entry.e:s;
});
SupplementCode存编码和实体的对应关系，SupplementCodeMatch用于生成正则表达式。在回调函数中查找对应的值并替换。
扩展其他实体符号只需要把SupplementCode和SupplementCodeMatch扩充即可。
