1.Object.prototype.toString()

使用typeof bar === "object"检测”bar”是否为对象有什么缺点？如何避免？

用 typeof 是否能准确判断一个对象变量，答案是否定的，null 的结果也是 object，数组的结果也是 object，有时候我们需要的是 "纯粹" 的 object 对象。如何避免呢？比较好的方式是： console.log(Object.prototype.toString.call(obj) === "[object Object]");

判断类型函数代码实现如下：

const getType = (obj) => Object.prototype.toString.call(obj).slice(8, -1);

export function isArray(obj: any): obj is any[] {
  return getType(obj) === 'Array';
}

export function isObject(obj: any): obj is { [key: string]: any } {
  return getType(obj) === 'Object';
}

export function isString(obj: any): obj is string {
  return getType(obj) === 'String';
}

export function isNumber(obj: any): obj is number {
  return getType(obj) === 'Number' && obj === obj;
}

export function isRegExp(obj: any) {
  return getType(obj) === 'RegExp';
}

export function isFile(obj: any): obj is File {
  return getType(obj) === 'File';
}

export function isBlob(obj: any): obj is Blob {
  return getType(obj) === 'Blob';
}

export function isUndefined(obj: any): obj is undefined {
  return obj === undefined;
}

export function isFunction(obj: any): obj is (...args: any[]) => any {
  return typeof obj === 'function';
}

export function isEmptyObject(obj: any): boolean {
  return isObject(obj) && Object.keys(obj).length === 0;
}