isPlainObject.js

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)
}

/**
 * Checks if `value` is object-like. A value is object-like if it's not `null`
 * and has a `typeof` result of "object".
 *
 * @since 4.0.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is object-like, else `false`.
 * @example
 *
 * isObjectLike({})
 * // => true
 *
 * isObjectLike([1, 2, 3])
 * // => true
 *
 * isObjectLike(Function)
 * // => false
 *
 * isObjectLike(null)
 * // => false
 */
function isObjectLike(value) {
	return typeof value == 'object' && value !== null
}

/**
 * Checks if `value` is a plain object, that is, an object created by the
 * `Object` constructor or one with a `[[Prototype]]` of `null`.
 *
 * @since 0.8.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is a plain object, else `false`.
 * @example
 *
 * function Foo() {
 *   this.a = 1
 * }
 *
 * isPlainObject(new Foo)
 * // => false
 *
 * isPlainObject([1, 2, 3])
 * // => false
 *
 * isPlainObject({ 'x': 0, 'y': 0 })
 * // => true
 *
 * isPlainObject(Object.create(null))
 * // => true
 */
function isPlainObject(value) {
	if (!isObjectLike(value) || getTag(value) != '[object Object]') {
		return false
	}
	if (Object.getPrototypeOf(value) === null) {
		return true
	}
	let proto = value
	while (Object.getPrototypeOf(proto) !== null) {
		proto = Object.getPrototypeOf(proto)
	}
	return Object.getPrototypeOf(value) === proto
}

export default isPlainObject