/* @flow */
// 创建空数组
export const emptyObject = Object.freeze({})
// These helpers produce better VM code in JS engines due to their
// explicitness and function inlining.
// 是否未定义
export function isUndef (v: any): boolean %checks {
return v === undefined || v === null
}
// 是否定义
export function isDef (v: any): boolean %checks {
return v !== undefined && v !== null
}
// 是否true
export function isTrue (v: any): boolean %checks {
return v === true
}
// 是否false
export function isFalse (v: any): boolean %checks {
return v === false
}
/**
* Check if value is primitive.
*/
// 是否原始基本类型
export function isPrimitive (value: any): boolean %checks {
return (
typeof value === 'string' ||
typeof value === 'number' ||
// $flow-disable-line
typeof value === 'symbol' ||
typeof value === 'boolean'
)
}
/**
* Quick object check - this is primarily used to tell
* Objects from primitive values when we know the value
* is a JSON-compliant type.
*/
// 是否是object
export function isObject (obj: mixed): boolean %checks {
return obj !== null && typeof obj === 'object'
}
/**
* Get the raw type string of a value, e.g., [object Object].
*/
// 复制原型toString方法，方面简写使用
const _toString = Object.prototype.toString
// 获得真正的类型，例如"[object Array]",结果为：Array， 也就是其数组构造器
export function toRawType (value: any): string {
return _toString.call(value).slice(8, -1)
}
/**
* Strict object type check. Only returns true
* for plain JavaScript objects.
*/
// 获得真正类型，是否是Object 对象
export function isPlainObject (obj: any): boolean {
return _toString.call(obj) === '[object Object]'
}
// 是否是RegExp 对象
export function isRegExp (v: any): boolean {
return _toString.call(v) === '[object RegExp]'
}
/**
* Check if val is a valid array index.
*/
// 是否有效的数组索引
export function isValidArrayIndex (val: any): boolean {
const n = parseFloat(String(val))
return n >= 0 && Math.floor(n) === n && isFinite(val)
}
// 是否promise对象
export function isPromise (val: any): boolean {
return (
isDef(val) &&
typeof val.then === 'function' &&
typeof val.catch === 'function'
)
}
/**
* Convert a value to a string that is actually rendered.
*/
// toString() 序列化{a:1, b:2} 形式等
export function toString (val: any): string {
return val == null
? ''
: Array.isArray(val) || (isPlainObject(val) && val.toString === _toString)
? JSON.stringify(val, null, 2)
: String(val)
}
/**
* Convert an input value to a number for persistence.
* If the conversion fails, return original string.
*/
// 转为数字
export function toNumber (val: string): number | string {
const n = parseFloat(val)
return isNaN(n) ? val : n
}
/**
* Make a map and return a function for checking if a key
* is in that map.
*/
// 创建个字典，返回函数检测key是否存在于map
export function makeMap (
str: string,
expectsLowerCase?: boolean
): (key: string) => true | void {
const map = Object.create(null)
const list: Array = str.split(',')
for (let i = 0; i < list.length; i++) {
map[list[i]] = true
}
return expectsLowerCase
? val => map[val.toLowerCase()]
: val => map[val]
}
/**
* Check if a tag is a built-in tag.
*/
// 检测标签tag是否是内置tag,比如 slot, component, 例如： isBuiltInTag('mytag') // undefined
export const isBuiltInTag = makeMap('slot,component', true)
/**
* Check if an attribute is a reserved attribute.
*/
// 检查属性是否为vue保留属性，key,ref,slot,slot-scope,is， 例如： isReservedAttribute('ref') // undefined
export const isReservedAttribute = makeMap('key,ref,slot,slot-scope,is')
/**
* Remove an item from an array.
*/
// 从数组中，删除一项
export function remove (arr: Array, item: any): Array | void {
if (arr.length) {
const index = arr.indexOf(item)
if (index > -1) {
return arr.splice(index, 1)
}
}
}
/**
* Check whether an object has the property.
*/
// 是否对象本身的属性，而非原型链上的
const hasOwnProperty = Object.prototype.hasOwnProperty
export function hasOwn (obj: Object | Array<*>, key: string): boolean {
return hasOwnProperty.call(obj, key)
}
/**
* Create a cached version of a pure function.
*/
// 创建个缓存函数
export function cached (fn: F): F {
const cache = Object.create(null)
return (function cachedFn (str: string) {
const hit = cache[str]
return hit || (cache[str] = fn(str))
}: any)
}
/**
* Camelize a hyphen-delimited string.
*/
// '-' 横线改为驼峰类型
const camelizeRE = /-(\w)/g
export const camelize = cached((str: string): string => {
return str.replace(camelizeRE, (_, c) => c ? c.toUpperCase() : '')
})
/**
* Capitalize a string.
*/
// 首字母大写
export const capitalize = cached((str: string): string => {
return str.charAt(0).toUpperCase() + str.slice(1)
})
/**
* Hyphenate a camelCase string.
*/
// 驼峰转横线形式
const hyphenateRE = /\B([A-Z])/g
export const hyphenate = cached((str: string): string => {
return str.replace(hyphenateRE, '-$1').toLowerCase()
})
/**
* Simple bind polyfill for environments that do not support it,
* e.g., PhantomJS 1.x. Technically, we don't need this anymore
* since native bind is now performant enough in most browsers.
* But removing it would mean breaking code that was able to run in
* PhantomJS 1.x, so this must be kept for backward compatibility.
*/
// 实现bind
/* istanbul ignore next */
function polyfillBind (fn: Function, ctx: Object): Function {
function boundFn (a) {
const l = arguments.length
return l
? l > 1
? fn.apply(ctx, arguments)
: fn.call(ctx, a)
: fn.call(ctx)
}
boundFn._length = fn.length
return boundFn
}
// 原生bind
function nativeBind (fn: Function, ctx: Object): Function {
return fn.bind(ctx)
}
// 兼容判断
export const bind = Function.prototype.bind
? nativeBind
: polyfillBind
/**
* Convert an Array-like object to a real Array.
*/
// 维数组转为真实数组
export function toArray (list: any, start?: number): Array {
start = start || 0
let i = list.length - start
const ret: Array = new Array(i)
while (i--) {
ret[i] = list[i + start]
}
return ret
}
/**
* Mix properties into target object.
*/
// 扩展集成
export function extend (to: Object, _from: ?Object): Object {
for (const key in _from) {
to[key] = _from[key]
}
return to
}
/**
* Merge an Array of Objects into a single Object.
*/
// 把对象数组中的对象提取到一个对象里面
export function toObject (arr: Array): Object {
const res = {}
for (let i = 0; i < arr.length; i++) {
if (arr[i]) {
extend(res, arr[i])
}
}
return res
}
/* eslint-disable no-unused-vars */
/**
* Perform no operation.
* Stubbing args to make Flow happy without leaving useless transpiled code
* with ...rest (https://flow.org/blog/2017/05/07/Strict-Function-Call-Arity/).
*/
export function noop (a?: any, b?: any, c?: any) {}
/**
* Always return false.
*/
export const no = (a?: any, b?: any, c?: any) => false
/* eslint-enable no-unused-vars */
/**
* Return the same value.
*/
export const identity = (_: any) => _
/**
* Generate a string containing static keys from compiler modules.
*/
export function genStaticKeys (modules: Array): string {
return modules.reduce((keys, m) => {
return keys.concat(m.staticKeys || [])
}, []).join(',')
}
/**
* Check if two values are loosely equal - that is,
* if they are plain objects, do they have the same shape?
*/
// 判断两个内容是否相同，非引用关系的判断
export function looseEqual (a: any, b: any): boolean {
if (a === b) return true
const isObjectA = isObject(a)
const isObjectB = isObject(b)
if (isObjectA && isObjectB) {
try {
const isArrayA = Array.isArray(a)
const isArrayB = Array.isArray(b)
if (isArrayA && isArrayB) {
return a.length === b.length && a.every((e, i) => {
return looseEqual(e, b[i])
})
} else if (a instanceof Date && b instanceof Date) {
return a.getTime() === b.getTime()
} else if (!isArrayA && !isArrayB) {
const keysA = Object.keys(a)
const keysB = Object.keys(b)
return keysA.length === keysB.length && keysA.every(key => {
return looseEqual(a[key], b[key])
})
} else {
/* istanbul ignore next */
return false
}
} catch (e) {
/* istanbul ignore next */
return false
}
} else if (!isObjectA && !isObjectB) {
return String(a) === String(b)
} else {
return false
}
}
/**
* Return the first index at which a loosely equal value can be
* found in the array (if value is a plain object, the array must
* contain an object of the same shape), or -1 if it is not present.
*/
// 返回数组元素的下标
export function looseIndexOf (arr: Array, val: mixed): number {
for (let i = 0; i < arr.length; i++) {
if (looseEqual(arr[i], val)) return i
}
return -1
}
/**
* Ensure a function is called only once.
*/
// 函数执行一次
export function once (fn: Function): Function {
let called = false
return function () {
if (!called) {
called = true
fn.apply(this, arguments)
}
}
}