SOURCE

const x = {
    'A': ['C', 'D'],
    'D': ['B'],
    'B': ['E'],
    'E': ['C', 'F']
}

const y = {
    'A': ['B', 'F'],
    'C': ['A', 'D'],
    'D': ['B'],
    'B': ['F']
}


function deal(obj, value){
    let result = []
    result.push(value)
    let dep = obj[value]
    for(let v in dep){
        let p = deal(obj, dep[v])
        for(let i = 0; i < p.length; i++){
            let index = result.indexOf(p[i])
            if(index > -1){
                result.splice(index, 1)
            }
        }
        result = result.concat(p)
    }
    return result
}

function dealDependency(obj){
    let r_arr = []
    let max_index = 0
    let max_length = 0
    let i = 0
    for(let key in obj){
        let r = deal(obj, key)
        if(r.length > max_length){
            max_length = r.length
            max_index = i
        }
       r_arr.push(r)
       i++
    }
    console.log(r_arr[max_index])
}

dealDependency(y)