cold-003判断一个对象有环引用

var obj = {
    a: {
        c: [
            1, 2
        ]
    },
    b: 1
}
obj.a.c.d = obj
console.log(cycleDetector(obj)) // true

function cycleDetector(obj) {
    const arr = [obj]
    let flag = false

    function cycle(o) {
        const keys = Object.keys(o)
        for (const key of keys) {
            const temp = o[key]
            if (typeof temp === 'object' && temp !== null) {
                if (arr.indexOf(temp) >= 0) {
                    flag = true
                    return
                }
                arr.push(temp)
                cycle(temp)
            }
        }
    }

    cycle(obj)

    return flag
}