vue/src/shared/util.js

/**
 * Convert a value to a string that is actually rendered.
 *
 * @param {*} val
 * @return {String}
 */
export function renderString (val) {
  return val == null
    ? ''
    : typeof val === 'object'
      ? JSON.stringify(val, null, 2)
      : String(val)
}

/**
 * Make a map and return a function for checking if a key
 * is in that map.
 *
 * @param {String} str
 * @param {Boolean} expectsLowerCase
 * @return {Function}
 */
export function makeMap (str, expectsLowerCase) {
  const map = Object.create(null)
  const list = 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.
 */
export const isBuiltInTag = makeMap('slot,component,render,transition', true)

/**
 * Remove an item from an array
 *
 * @param {Array} arr
 * @param {*} item
 */
export function remove (arr, item) {
  if (arr.length) {
    const index = arr.indexOf(item)
    if (index > -1) {
      return arr.splice(index, 1)
    }
  }
}

/**
 * Check whether the object has the property.
 *
 * @param {Object} obj
 * @param {String} key
 * @return {Boolean}
 */
const hasOwnProperty = Object.prototype.hasOwnProperty
export function hasOwn (obj, key) {
  return hasOwnProperty.call(obj, key)
}

/**
 * Check if value is primitive
 *
 * @param {*} value
 * @return {Boolean}
 */
export function isPrimitive (value) {
  return typeof value === 'string' || typeof value === 'number'
}

/**
 * Create a cached version of a pure function.
 *
 * @param {Function} fn
 * @return {Function}
 */
export function cached (fn) {
  const cache = Object.create(null)
  return function cachedFn (str) {
    const hit = cache[str]
    return hit || (cache[str] = fn(str))
  }
}

/**
 * Camelize a hyphen-delmited string.
 *
 * @param {String} str
 * @return {String}
 */
const camelizeRE = /-(\w)/g
export const camelize = cached(str => {
  return str.replace(camelizeRE, toUpper)
})

function toUpper (_, c) {
  return c ? c.toUpperCase() : ''
}

/**
 * Hyphenate a camelCase string.
 *
 * @param {String} str
 * @return {String}
 */
const hyphenateRE = /([a-z\d])([A-Z])/g
export const hyphenate = cached(str => {
  return str
    .replace(hyphenateRE, '$1-$2')
    .toLowerCase()
})

/**
 * Simple bind, faster than native
 *
 * @param {Function} fn
 * @param {Object} ctx
 * @return {Function}
 */
export function bind (fn, ctx) {
  return function (a) {
    const l = arguments.length
    return l
      ? l > 1
        ? fn.apply(ctx, arguments)
        : fn.call(ctx, a)
      : fn.call(ctx)
  }
}

/**
 * Convert an Array-like object to a real Array.
 *
 * @param {Array-like} list
 * @param {Number} [start] - start index
 * @return {Array}
 */
export function toArray (list, start) {
  start = start || 0
  let i = list.length - start
  const ret = new Array(i)
  while (i--) {
    ret[i] = list[i + start]
  }
  return ret
}

/**
 * Mix properties into target object.
 *
 * @param {Object} to
 * @param {Object} from
 */
export function extend (to, _from) {
  for (const key in _from) {
    to[key] = _from[key]
  }
  return to
}

/**
 * Quick object check - this is primarily used to tell
 * Objects from primitive values when we know the value
 * is a JSON-compliant type.
 *
 * @param {*} obj
 * @return {Boolean}
 */
export function isObject (obj) {
  return obj !== null && typeof obj === 'object'
}

/**
 * Strict object type check. Only returns true
 * for plain JavaScript objects.
 *
 * @param {*} obj
 * @return {Boolean}
 */
const toString = Object.prototype.toString
const OBJECT_STRING = '[object Object]'
export function isPlainObject (obj) {
  return toString.call(obj) === OBJECT_STRING
}

/**
 * Array type check.
 *
 * @param {*} obj
 * @return {Boolean}
 */
export const isArray = Array.isArray