Question

Doing some client-side JavaScript development, which requires me to call a client-side API which only accepts one parameter at a time (cough, cough, facebook).

Basically i need to call an API method twice:

someFBApi.requestPerms('email')
someFBApi.requestPerms('publish_stream')

Now, i have a wrapper function for this call which looks like this:

function requestPermission(permission, callback) {
 someFBApi.requestPerms(permission, callback);
}

But the problem is, i have to call the function “requestPermission” twice from all over the place:

requestPermission('email', function(perm1granted) {
   requestPermission('publish_stream', function(perm2granted) {
      // do something with perm 1 and perm 2

I would like to be able to do this:

requestPermissions('email,publish_stream', function(firstPerm,secondPerm) {
   // do something with firstPerm, secondPerm

I know i have to call FB API twice (fine), but i want that ‘doubling up’ to occur in that function (not all over the place). Know what i mean?

So, i’ll accept an answer of two forms:

• Can i pass an array of strings, iterate through those? (maybe JSON?)
• Delimeted-string, then split the string in the function.

Keep in mind the function returns a value indicating whether or not the permission was granted. So it needs to accept an array/delimited list of strings and return an array/delimited list of strings.

The more simple the solution, the better. (jQuery fine)

Answer 1

Don’t be tempted to use the string parsing solution. An array is cleaner and simpler:

/* note: permisions is expected to be an array */
function requestPermission(permissions) {
    for (var i=0; i<permissions.length; i++) {
        doSomething(permissions[i]);
    }
}

Now, the only problem would seem to be what to do with the callback. I’m assuming that the API is asynchronous and you’d want something like this:

doSomething(when_done)->doSomething...(finally)->execute_callback

For that you can use a sort of recursion. Except it wouldn’t really be recursion in the traditional sense since each call happen asynchronously. Something like:

/* note: permisions is expected to be an array */
function requestPermission(permissions,callback) {
    var p = permissions.shift();
    var f = callback;
    if (permissions.length > 0) {
        // if this is not the last permission then
        // call this function again in the callback:
        f = function () {
            requestPermission(permissions,callback);
        }
    }
    someFBApi.requestPerms(p,f);
}

Now you can use it like this:

requestPermissions(['email','publish_stream'],finalCallback);