function compress(source) {

    const keys = {}; ⇽--- 存储目标key

    source.replace(

    /([^=&]+)=([^&]*)/g,

    function(full, key, value) { ⇽--- 提取键值对信息

        keys[key] =(keys[key] ? keys[key] + "," : "") + value;

        return "";

    }

);

const result = [];

for (let key in keys) {

    result.push(key + "=" + keys[key]);

    } ⇽--- 收集key信息

    return result.join("&"); ⇽--- 使用&符号链接结果

}

assert(compress("foo=1&foo=2&blah=a&blah=b&foo=3") === "foo=1,2,3&blah=a,b","Compression is OK!");