#736 Fill In a Route

Links in a single-page app are built from route patterns, like /users/:id/posts/:postId with { id: 42, postId: "a b" } giving /users/42/posts/a%20b.

Write buildPath(pattern, params). Split the pattern on / and ignore empty pieces. Keep plain segments as they are, and replace each :name segment with encodeURIComponent(String(params[name])). Join the segments with / and put a / in front; a pattern with no segments gives "/". If any parameter is missing from params, return null. Extra entries in params are ignored.

Input: pattern = "/users/:id/posts/:postId", params = {"id":42,"postId":"a b"}
Output: "/users/42/posts/a%20b"

Input: pattern = "/users/:id", params = {}
Output: null

Constraints

• Patterns are 1 to 200 characters and contain no *.
• Parameter values are strings or numbers.