refactor: strictly typed

src/fs/browser.ts

@@ -1,7 +1,7 @@
 import { last } from '../util/underscore'
 import IFS from './ifs'
 
-function domResolve (root, path) {
+function domResolve (root: string, path: string) {
   const base = document.createElement('base')
   base.href = root
 
@@ -16,7 +16,7 @@ function domResolve (root, path) {
   return resolved
 }
 
-function resolve (root, filepath, ext) {
+function resolve (root: string, filepath: string, ext: string) {
   if (root.length && last(root) !== '/') root += '/'
   const url = domResolve(root, filepath)
   return url.replace(/^(\w+:\/\/[^/]+)(\/[^?]+)/, (str, origin, path) => {

src/fs/ifs.ts

@@ -1,5 +1,5 @@
 export default interface IFS {
-  exists: (filepath?: string) => Promise<boolean>
+  exists: (filepath: string) => Promise<boolean>
   readFile: (filepath:string) => Promise<string>
   resolve: (root: string, file: string, ext: string) => string
 }

src/fs/node.ts

@@ -3,11 +3,11 @@ import { resolve, extname } from 'path'
 import { stat, readFile } from 'fs'
 import IFS from './ifs'
 
-const statAsync = _.promisify(stat) as (filepath: string) => Promise<object>
-const readFileAsync = _.promisify(readFile) as (filepath: string, encoding: string) => Promise<string>
+const statAsync = _.promisify(stat)
+const readFileAsync = _.promisify<string, string, string>(readFile)
 
 const fs: IFS = {
-  exists: filepath => {
+  exists: (filepath: string) => {
     return statAsync(filepath).then(() => true).catch(() => false)
   },
   readFile: filepath => {