Is a number "in" another number?

Additive codes based on linux file/directory permissions

[ocon]

I'm trying to determine if a product code is allowed to be transported by a set transportation mode. The transportation codes are based on the following table:

Car = 1
Truck = 2
Train = 4

I might be given the code of 1 which means the item can be transported by Car, 3 means it can go by Car or Truck (1+2=3), or 7 means it can go by Car, Truck or Train (1+2+4=7), and so forth.

How can I make this work?

var transmode = 5;
if(productcode "in" transmode){do something;}

[Fotiman]

This is a bitmask.
Consider these numbers when they are converted to binary (note, I'm using 8 bits for these... because showing all 32 bits is not useful for this demonstration):
1 = 00000001
2 = 00000010
3 = 00000011
4 = 00000100
5 = 00000101
6 = 00000110
7 = 00000111

So can do bitwise & (AND) operations to determine if one of these flags is set. For example:

var Car = 1,
  Truck = 2,
  Train = 4;

var transmode = 5; // 00000101, aka: Car + Train
if (Car & transmode) {
  // do something
}

More info on Bitwise operators available:
[developer.mozilla.org...]

[lucy24]

... and if you have trouble internalizing 2 4 8 16 32 etcetera,* you can call the successive modes 1 2 3 etcetera and express it as Math.pow(2,whatever-the-syntax-is) ;)



* My brain gives out around 4096.

[ocon]

That's awesome, thank you. I knew it was based on the binary position but I had no idea of the bitwise operator, in fact I had to reread that multiple times because always converted it to && (logical and). This saves me from an if/else hell, thanks.