工具函数

摘抄自 Vue/util/lang

对象路径取值

export function parsePath(path: string): any {
  if (bailRE.test(path)) {
    return
  }
  const segments = path.split('.')
  return function(obj) {
    for (let i = 0; i < segments.length; i++) {
      if (!obj) return
      obj = obj[segments[i]]
    }
    return obj
  }
}

\$ 或者 \_ 开头

export function isReserved(str: string): boolean {
  const c = (str + '').charCodeAt(0)
  return c === 0x24 || c === 0x5f
}

摘抄自 Vue/share/util

基础类型判断

export function isUndef(v: any): boolean %checks {
  return v === undefined || v === null
}

export function isDef(v: any): boolean %checks {
  return v !== undefined && v !== null
}

export function isTrue(v: any): boolean %checks {
  return v === true
}

export function isFalse(v: any): boolean %checks {
  return v === false
}

// 是否是原始类型
export function isPrimitive(value: any): boolean %checks {
  return (
    typeof value === 'string' ||
    typeof value === 'number' ||
    // $flow-disable-line
    typeof value === 'symbol' ||
    typeof value === 'boolean'
  )
}

// 是否是对象
export function isObject(obj: mixed): boolean %checks {
  return obj !== null && typeof obj === 'object'
}

// 是否是promise
export function isPromise(val: any): boolean {
  return isDef(val) && typeof val.then === 'function' && typeof val.catch === 'function'
}

利用 toString 判断类型

const _toString = Object.prototype.toString
export function toRawType(value: any): string {
  return _toString.call(value).slice(8, -1)
}
export function isPlainObject(obj: any): boolean {
  return _toString.call(obj) === '[object Object]'
}
export function isRegExp(v: any): boolean {
  return _toString.call(v) === '[object RegExp]'
}

类型转换

export function toString(val: any): string {
  return val == null ? '' : Array.isArray(val) || (isPlainObject(val) && val.toString === _toString) ? JSON.stringify(val, null, 2) : String(val)
}

export function toNumber(val: string): number | string {
  const n = parseFloat(val)
  return isNaN(n) ? val : n
}

缓存

export function cached<F: Function>(fn: F): F {
  const cache = Object.create(null)
  return (function cachedFn(str: string) {
    const hit = cache[str]
    return hit || (cache[str] = fn(str))
  }: any)
}

capitalize

export const capitalize = cached((str: string): string => {
  return str.charAt(0).toUpperCase() + str.slice(1)
})

bind

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
}

数组对象互转

export function toArray(list: any, start?: number): Array<any> {
  start = start || 0
  let i = list.length - start
  const ret: Array<any> = new Array(i)
  while (i--) {
    ret[i] = list[i + start]
  }
  return ret
}

export function extend(to: Object, _from: ?Object): Object {
  for (const key in _from) {
    to[key] = _from[key]
  }
  return to
}

export function toObject(arr: Array<any>): Object {
  const res = {}
  for (let i = 0; i < arr.length; i++) {
    if (arr[i]) {
      extend(res, arr[i])
    }
  }
  return res
}

once

export function once(fn: Function): Function {
  let called = false
  return function() {
    if (!called) {
      called = true
      fn.apply(this, arguments)
    }
  }
}

looseEqual

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
  }
}

export function once(fn: Function): Function {
  let called = false
  return function() {
    if (!called) {
      called = true
      fn.apply(this, arguments)
    }
  }
}