老师，我试了一下不在声明 result 的时候赋默认值为空对象，在下方判断传入参数为对象是再赋值，就会死循环，这是为什么呢？

export function cloneDeep (obj: any, map = new WeakMap()):any {
    if (typeof obj !== 'object' || obj == null) return obj

    if (map.get(obj)) {
        return map.get(obj)
    }

    let result: any // 暂不赋值，在下方判断是 obj 为对象后再赋值
    map.set(obj, result)


    if (obj instanceof Map) {
        result = new Map()
        obj.forEach((v, k) => {
            const key = cloneDeep(k, map)
            const value = cloneDeep(v, map)
            result.set(key, value)
        })
    }

    if (obj instanceof Set) {
        result = new Set()
        obj.forEach(v => {
            const value = cloneDeep(v, map)
            result.add(value)
        })
    }

    if (obj instanceof Array) {
        result = []
        result = obj.map(item => cloneDeep(item, map))
    }

    if (Object.prototype.toString.call(obj) === '[object Object]') {
        result = {} // 这里赋值
        for (const key in obj) {
            const val = obj[key]
            const val1 = cloneDeep(val, map)
            result[key] = val1
        }
    }

    return result
}

其他的代码都没变