深拷贝

function deepClone(startObj, endObj) {
    let obj = endObj || {};
    for (let i in startObj) {
        if (typeof startObj[i] === 'object') {
            obj[i] = startObj[i].constructor === Array ? [] : {};
            deepClone(startObj[i], obj[i])
        } else {
            obj[i] = startObj[i];
        }
    }
    return obj;
}
方式1 递归 deepClone

方式2 let b = JSON.parse(JSON.stringify(a))