地址栏参数的解析

var paramsString = "q=URLUtils.searchParams&topic=api"

var searchParams = new URLSearchParams(paramsString);

for (let p of searchParams) {

　　console.log(p);

}

searchParams.has("topic") === true; // true

searchParams.get("topic") === "api"; // true

searchParams.getAll("topic"); // ["api"]

searchParams.get("foo") === ""; // true

searchParams.append("topic", "webdev");

searchParams.toString(); // "q=URLUtils.searchParams&topic=api&topic=webdev"

searchParams.set("topic", "More webdev");

searchParams.toString(); // "q=URLUtils.searchParams&topic=More+webdev"

searchParams.delete("topic");

searchParams.toString(); // "q=URLUtils.searchParams"