Vue 是如何实现配置选项多种写法的，如 props inject 等选项既支持数组 + 字符串写法也支持对象写法。
看了源码发现有一个格式化的过程，不管是哪种类型的写法，最后都会格式化为统一的形式。
附上 props inject 格式化代码
/**
* Ensure all props option syntax are normalized into the
* Object-based format.
*/
function normalizeProps (options: Object, vm: ?Component) {
const props = options.props
if (!props) return
const res = {}
let i, val, name
if (Array.isArray(props)) {
i = props.length
while (i--) {
val = props[i]
if (typeof val === 'string') {
name = camelize(val)
res[name] = { type: null }
} else if (process.env.NODE_ENV !== 'production') {
warn('props must be strings when using array syntax.')
}
}
} else if (isPlainObject(props)) {
for (const key in props) {
val = props[key]
name = camelize(key)
res[name] = isPlainObject(val)
? val
: { type: val }
}
} else if (process.env.NODE_ENV !== 'production') {
warn(
`Invalid value for option "props": expected an Array or an Object, ` +
`but got ${toRawType(props)}.`,
vm
)
}
options.props = res
}
/**
* Normalize all injections into Object-based format
*/
function normalizeInject (options: Object, vm: ?Component) {
const inject = options.inject
if (!inject) return
const normalized = options.inject = {}
if (Array.isArray(inject)) {
for (let i = 0; i < inject.length; i++) {
normalized[inject[i]] = { from: inject[i] }
}
} else if (isPlainObject(inject)) {
for (const key in inject) {
const val = inject[key]
normalized[key] = isPlainObject(val)
? extend({ from: key }, val)
: { from: val }
}
} else if (process.env.NODE_ENV !== 'production') {
warn(
`Invalid value for option "inject": expected an Array or an Object, ` +
`but got ${toRawType(inject)}.`,
vm
)
}
}
