lodash-at

const toString = Object.prototype.toString

/**
 * Gets the `toStringTag` of `value`.
 *
 * @private
 * @param {*} value The value to query.
 * @returns {string} Returns the `toStringTag`.
 */
function getTag(value) {
  if (value == null) {
    return value === undefined ? '[object Undefined]' : '[object Null]'
  }
  return toString.call(value)
}

export default getTag

getTag,万能获取类型方法

import getTag from './.internal/getTag.js'

/**
 * Checks if `value` is classified as a `Symbol` primitive or object.
 *
 * @since 4.0.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is a symbol, else `false`.
 * @example
 *
 * isSymbol(Symbol.iterator)
 * // => true
 *
 * isSymbol('abc')
 * // => false
 */
function isSymbol(value) {
  const type = typeof value
  return type == 'symbol' || (type === 'object' && value != null && getTag(value) == '[object Symbol]')
}

export default isSymbol

如果为symbol类型,那么肯定就是symbol,如果是对象且不为null,得到tag为[object, symbol],也一定为symbol

import isSymbol from '../isSymbol.js'

/** Used to match property names within property paths. */
const reIsDeepProp = /\.|\[(?:[^[\]]*|(["'])(?:(?!\1)[^\\]|\\.)*?\1)\]/
const reIsPlainProp = /^\w*$/

/**
 * Checks if `value` is a property name and not a property path.
 *
 * @private
 * @param {*} value The value to check.
 * @param {Object} [object] The object to query keys on.
 * @returns {boolean} Returns `true` if `value` is a property name, else `false`.
 */
function isKey(value, object) {
//数组不能作为key值
  if (Array.isArray(value)) {
    return false
  }
  const type = typeof value
   // 数字,布尔,null和symbol可以作为key值
  if (type === 'number' || type === 'boolean' || value == null || isSymbol(value)) {
    return true
  }
  return reIsPlainProp.test(value) || !reIsDeepProp.test(value) ||
    (object != null && value in Object(object))
}

export default isKey

不能是这些特殊字符