深拷贝

// 深拷贝（尤雨溪版） function find(list, f) { return list.filter(f)[0] }

function deepCopy(obj, cache = []) { // just return if obj is immutable value if (obj === null || typeof obj !== 'object') { return obj }

// if obj is hit, it is in circular structure
const hit = find(cache, c => c.original === obj)
if (hit) {
    return hit.copy
}

const copy = Array.isArray(obj) ? [] : {}
// put the copy into cache at first
// because we want to refer it in recursive deepCopy
cache.push({
    original: obj,
    copy
})
Object.keys(obj).forEach(key => copy[key] = deepCopy(obj[key], cache))

return copy

}