replace + split

'{"A":"5","B":"4","C":"3","D":"2"}'.replace(/(?:"[^"]+":)|["{}]/g,'').split(',')
["5", "4", "3", "2"]

split

str = '{"A":"5","B":"4","C":"3","D":"2"}';
str.split(/(?:^\{|",)"[^"]+":"|"\}$/g).slice(1,-1)
["5", "4", "3", "2"]

简化~

str.split(/[{"][^:]+:"|"\}/g).slice(1,-1)
["5", "4", "3", "2"]

const str = '{"A":"5","B":"4","C":"3","D":"2"}';
const obj = JSON.parse(str)
const keys = Object.keys(obj) 

var obj=JSON.parse('{"A":"5","B":"4","C":"3","D":"2"}');
for(var k in obj){
console.log(k)
}

let obj = {"A":"5", "B":"4", "C":"3", "D":"2"};

alert(Object.keys(obj).join(""));

转成json对象，然后根据key取value

 '{"A":"5","B":"4","C":"3","D":"2"}'.match(/"\w+"\:/g).map(function(el){return el.slice(1,-2)})


["A", "B", "C", "D"]

var str = '{"A":"5","B":"4","C":"3","D":"2"}';
var obj = JSON.parse(str);
var arr=[];
for(var key in obj){arr.push(obj[key])}

["5", "4", "3", "2"]

var str = '{"A":"5","B":"4","C":"3","D":"2"}';
var obj = JSON.parse(str)
for (key in obj) {
    console.log(obj[key])
} 

var str = '{"A":"5","B":"4","C":"3","D":"2"}';
var str=JSON.parse(str);
var b=[];
for(key in str){
   b.push(key);
}
console.log(b)//["A", "B", "C", "D"]