const obj = {
    goods: {
        name: 'a',
        tags: {
            name: '快速',
            id: 1,
            tagType: {
                name: '標(biāo)簽'
            }
        }
    }
}

if (obj.goods !== null
    && obj.goods.tags !== null
    && obj.goods.tags.tagType !== null) {
  
}

let name = obj?.goods?.tags?.tageType?.name;

_.get(object, path, [defaultValue])

var object = { 'a': [{ 'b': { 'c': 3 } }] };
​
_.get(object, 'a[0].b.c');
// => 3 
​
_.get(object, ['a', '0', 'b', 'c']);
// => 3
​
_.get(object, 'a.b.c', 'default');
// => 'default'

function get(object, path, defaultValue) {
  const result = object == null ? undefined : baseGet(object, path)
  return result === undefined ? defaultValue : result
}

function baseGet(object, path) {
  // 將輸入的字符串路徑轉(zhuǎn)換成數(shù)組，
  path = castPath(path, object)
​
  let index = 0
  const length = path.length
  // 遍歷數(shù)組獲取每一層對(duì)象
  while (object != null && index < length) {
    object = object[toKey(path[index++])] // toKey方法
  }
  return (index && index == length) ? object : undefined
}
​

/** Used as references for various `Number` constants. */
const INFINITY = 1 / 0
​
/**
 * Converts `value` to a string key if it's not a string or symbol.
 *
 * @private
 * @param {*} value The value to inspect.
 * @returns {string|symbol} Returns the key.
 */
function toKey(value) {
  if (typeof value === 'string' || isSymbol(value)) {
    return value
  }
  const result = `${value}`
  return (result == '0' && (1 / value) == -INFINITY) ? '-0' : result
}

import isKey from './isKey.js'
import stringToPath from './stringToPath.js'
​
/**
 * Casts `value` to a path array if it's not one.
 *
 * @private
 * @param {*} value The value to inspect.
 * @param {Object} [object] The object to query keys on.
 * @returns {Array} Returns the cast property path array.
 */
function castPath(value, object) {
  if (Array.isArray(value)) {
    return value
  }
  return isKey(value, object) ? [value] : stringToPath(value)
}
​

import memoizeCapped from './memoizeCapped.js'
​
const charCodeOfDot = '.'.charCodeAt(0)
const reEscapeChar = /\(\)?/g
const rePropName = RegExp(
  // Match anything that isn't a dot or bracket.
  '[^.[\]]+' + '|' +
  // Or match property names within brackets.
  '\[(?:' +
    // Match a non-string expression.
    '([^"'][^[]*)' + '|' +
    // Or match strings (supports escaping characters).
    '(["'])((?:(?!\2)[^\\]|\\.)*?)\2' +
  ')\]'+ '|' +
  // Or match "" as the space between consecutive dots or empty brackets.
  '(?=(?:\.|\[\])(?:\.|\[\]|$))'
  , 'g')
​
/**
 * Converts `string` to a property path array.
 *
 * @private
 * @param {string} string The string to convert.
 * @returns {Array} Returns the property path array.
 */
const stringToPath = memoizeCapped((string) => {
  const result = []
  if (string.charCodeAt(0) === charCodeOfDot) {
    result.push('')
  }
  string.replace(rePropName, (match, expression, quote, subString) => {
    let key = match
    if (quote) {
      key = subString.replace(reEscapeChar, '$1')
    }
    else if (expression) {
      key = expression.trim()
    }
    result.push(key)
  })
  return result
})
​

import memoize from '../memoize.js'
​
/** Used as the maximum memoize cache size. */
const MAX_MEMOIZE_SIZE = 500
​
/**
 * A specialized version of `memoize` which clears the memoized function's
 * cache when it exceeds `MAX_MEMOIZE_SIZE`.
 *
 * @private
 * @param {Function} func The function to have its output memoized.
 * @returns {Function} Returns the new memoized function.
 */
function memoizeCapped(func) {
  const result = memoize(func, (key) => {
    const { cache } = result
    if (cache.size === MAX_MEMOIZE_SIZE) {
      cache.clear()
    }
    return key
  })
​
  return result
}
​
export default memoizeCapped
​

function memoize(func, resolver) {
  if (typeof func !== 'function' || (resolver != null && typeof resolver !== 'function')) {
    throw new TypeError('Expected a function')
  }
  const memoized = function(...args) {
    const key = resolver ? resolver.apply(this, args) : args[0]
    const cache = memoized.cache
​
    if (cache.has(key)) {
      return cache.get(key)
    }
    const result = func.apply(this, args)
    memoized.cache = cache.set(key, result) || cache
    return result
  }
  memoized.cache = new (memoize.Cache || Map)
  return memoized
}
​
memoize.Cache = Map

/**
   * Gets the value at `path` of `object`. If the resolved value is
   * `undefined`, the `defaultValue` is returned in its place.
   * @example
   * const object = { 'a': [{ 'b': { 'c': 3 } }] }
   *
   * get(object, 'a[0].b.c')
   * // => 3
   *
   * get(object, ['a', '0', 'b', 'c'])
   * // => 3
   *
   * get(object, 'a.b.c', 'default')
   * // => 'default'
   */
  safeGet (object, path, defaultValue) {
    let result
    if (object != null) {
      if (!Array.isArray(path)) {
        const type = typeof path
        if (type === 'number' || type === 'boolean' || path == null ||
        /^\w*$/.test(path) || !(/.|[(?:[^[]]*|(["'])(?:(?!\1)[^\]|\.)*?\1)]/.test(path)) ||
        (object != null && path in Object(object))) {
          path = [path]
        } else {
          const result = []
          if (path.charCodeAt(0) === '.'.charCodeAt(0)) {
            result.push('')
          }
          const rePropName = RegExp(
            // Match anything that isn't a dot or bracket.
            '[^.[\]]+|\[(?:([^"'][^[]*)|(["'])((?:(?!\2)[^\\]|\\.)*?)\2)\]|(?=(?:\.|\[\])(?:\.|\[\]|$))'
            , 'g')
          path.replace(rePropName, (match, expression, quote, subString) => {
            let key = match
            if (quote) {
              key = subString.replace(/\(\)?/g, '$1')
            } else if (expression) {
              key = expression.trim()
            }
            result.push(key)
          })
          path = result
        }
      }
      let index = 0
      const length = path.length
      const toKey = (value) => {
        if (typeof value === 'string') {
          return value
        }
        const result = `${value}`
        return (result === '0' && (1 / value) === -(1 / 0)) ? '-0' : result
      }
      while (object != null && index < length) {
        object = object[toKey(path[index++])]
      }
      result = (index && index === length) ? object : undefined
    }
    return result === undefined ? defaultValue : result
  }