如何使用二进制系统（1,2,4）作为算法？

Question

Similar to chmod, I would like to use 1, 2, 4 as a way of notifications.

1 = Email 
2 = SMS 
4 = Push notifications

Is there function (preferably in javascript) that can input a number (above) and can return an object with:

{
    email: true,
    sms: true,
    push: false
}

I want the function to not be hard coded. I don't want a bunch of if statements that check for every combination there is. I want a "smart" way to do it.

Answer 1

How about something like this:

var commsMode = {
    email: 1,
    sms: 2,
    push: 4,
    toObject: function(val){
        var rt = {};

        for (e in commsMode) {
            rt[e] = (val & commsMode[e]) > 0;
        }

        return rt;
    }
};

var obj = commsMode.toObject(3);

Working example here .

Extended example:

var commsMode = {
    email: 1,
    sms: 2,
    push: 4,
    mode4: 8,
    mode5: 16,
    mode6: 32,
    mode7: 64,
    mode8: 128,
    toObject: function(val){
        var rt = {};

        for (e in commsMode) {
            rt[e] = (val & commsMode[e]) > 0;
        }

        return rt;
    }
};

var obj = commsMode.toObject(233);

for (p in obj) {
    alert(p + ': ' + obj[p])
}

Working example here

Answer 2

Try something like this - sorry, this is Python, but the JavaScript translation should be very similar:

def notifications(mask):
    return {
        'email' : mask & 4 != 0,
        'sms'   : mask & 2 != 0,
        'push'  : mask & 1 != 0
    }

notifications(0b111) # same as notifications(7), or notifications(email+sms+push)
=> {'push': True, 'sms': True, 'email': True}

In the above, we're saying that the notifications binary bit mask is 0b111 (or 7, if you prefer to use base-10), meaning that all three notifications are enabled. Similarly, if we had passed as bit mask 0b010 (or 2 in base-10), then the answer would have been:

notifications(0b010) # same as notifications(2), or notifications(sms)
=> {'push': False, 'sms': True, 'email': False}

Answer 3

Solution with multiple parameters to send to function:

var states = {
  '1': 'email',
  '2': 'sms',
  '4': 'push'
};

function getStates(){
 var o = {};
 for(var val in states){
   o[states[val]] = false;   
 }

   for(var i=0;i<arguments.length;i++){
     var arg = arguments[i];  
     var state = states[arg];
      if(state){
        o[state] = true;
      }  
  }

  return o;
}

console.log(getStates()); // return {email: false, sms: false, push: false}
console.log(getStates(1,2)); // return {email: true, sms: true, push: false} 

http://jsfiddle.net/ZTA6E/