js replace如何做变量替换呢？

Question

例如
string = '${1} = ${2} + ${3}'
替换为
string = '${1} = ${2} + ${3#a1}'
目前我的方案是将${3}作为变量去string中做匹配

let a = '${3}'
string.replace(new RegExp(a,'g'),xxx)

但是报了如下的错误，请问这是什么原因呢？

Answer 1

按字符串替换

var string = '${1} = ${2} + ${3}+${3}';

let a = '${3}'
string.replaceAll(a,'${3#a1}');
//'${1} = ${2} + ${3#a1}+${3#a1}'

JavaScript正则表达式需要转义的字符
https://blog.csdn.net/weixin_...

//可无脑转义元字符
var string = "^$.*+?|\\/[]{}=!:-,";
var regex = /\^\$\.\*\+\?\|\\\/\[\]\{\}\=\!\:\-\,/;

按正则替换

var string = '${1} = ${2} + ${3}+${3}';

let a = '\\$\\{3\\}'
string.replace(new RegExp(a,'g'),'${3#a1}');
//'${1} = ${2} + ${3#a1}+${3#a1}'

Answer 2

如果你只是不替换${2}且${1}之类不太多，比如只有${9}以下，还是比较好替换的

oldString =  '${1} = ${2} + ${3}'
newString = oldString.replaceAll(/(?<=\$\{)[^2](?=\})/g,'$&#a1')