实现宽松相等 looseEqual ​

// source: vue2/shared
function isObject(obj) {
  return obj !== null && typeof obj === 'object'
}

/**
 * Check if two values are loosely equal - that is,
 * if they are plain objects, do they have the same shape?
 */
function looseEqual(a, b) {
  if (a === b) {
    return true
  }
  var isObjectA = isObject(a)
  var isObjectB = isObject(b)
  if (isObjectA && isObjectB) {
    try {
      var isArrayA = Array.isArray(a)
      var isArrayB = Array.isArray(b)
      if (isArrayA && isArrayB) {
        return (
          a.length === b.length &&
          a.every(function (e, i) {
            return looseEqual(e, b[i])
          })
        )
      } else if (a instanceof Date && b instanceof Date) {
        return a.getTime() === b.getTime()
      } else if (!isArrayA && !isArrayB) {
        var keysA = Object.keys(a)
        var keysB = Object.keys(b)
        return (
          keysA.length === keysB.length &&
          keysA.every(function (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.
 */
function looseIndexOf(arr, val) {
  for (var i = 0; i < arr.length; i++) {
    if (looseEqual(arr[i], val)) {
      return i
    }
  }
  return -1
}