refactor: option merging + extract helper functions

packages/shared/README.md

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+# @vue/shared

packages/shared/package.json

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+{
+  "name": "@vue/shared",
+  "private": true
+}

packages/shared/src/index.ts

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+export const EMPTY_OBJ: { readonly [key: string]: any } = Object.freeze({})
+
+export const NOOP = () => {}
+
+export const onRE = /^on/
+export const vnodeHookRE = /^vnode/
+export const handlersRE = /^on|^vnode/
+export const reservedPropRE = /^(?:key|ref|slots)$|^vnode/
+
+export const isArray = Array.isArray
+export const isFunction = (val: any): val is Function =>
+  typeof val === 'function'
+export const isString = (val: any): val is string => typeof val === 'string'
+export const isObject = (val: any): val is Record<any, any> =>
+  val !== null && typeof val === 'object'
+
+const camelizeRE = /-(\w)/g
+export const camelize = (str: string): string => {
+  return str.replace(camelizeRE, (_, c) => (c ? c.toUpperCase() : ''))
+}
+
+const hyphenateRE = /\B([A-Z])/g
+export const hyphenate = (str: string): string => {
+  return str.replace(hyphenateRE, '-$1').toLowerCase()
+}
+
+export const capitalize = (str: string): string => {
+  return str.charAt(0).toUpperCase() + str.slice(1)
+}