compare two arrays if keys match with underscore.js

Question

I have an array with permissions from Facebook and an array of the permissions that the user shouldve given:

window.FB.api('/me/permissions', function(perm){                     
    if(perm){
       var given_permissions =  _.keys(perm['data'][0];
       var needed_permissions = ["publish_stream", "email"];
       //now check if given permissions contains needed permissions
    }
}

Now I want to compare if all the needed_permissions are in given_permissions, in an underscore savvy way (without looping two arrays myself and compare values). I saw a _.include method, but this compares an array with a value. I want to return true if all the permissions are available and else a false. I was looking for a nice single line call if possible.

The reason for this is, that FB.login returns true even if the user chooses to cancel the extended permissions. So I need to doublecheck this.

Answer 1

You could use _.difference to see if removing the given permissions from your required permissions leaves anything behind:

var diff = _(needed_permissions).difference(given_permissions)
if(diff.length > 0)
    // Some permissions were not granted

A nice side effect of this is that you get the missing permissions in diff in case you want to tell them what's wrong.

Answer 2

How about this?

_.all(needed_permissions, function(v){
    return _.include(given_permissions, v);
});