function sum(n) { if (n === 1) return 1 return n + sum(n - 1) //相当于 return 100 + 99 + 98 + ... + 1 } sum(100)//5050
function deepClone(sourceObj) { if (!sourceObj || typeof sourceObj !== 'object' || Object.keys(sourceObj).length === undefined) { return sourceObj } const cloneObj = sourceObj instanceof Array ? [] : { } Object.keys(sourceObj).forEach(obj => { cloneObj[obj] = deepClone(sourceObj[obj]) }) return cloneObj } let newObj = deepClone(obj)//深拷贝后的新对象