Javascript, syntax after function

Question

I have a function that changes an object for me and I'm wondering how a bit of it works and would be grateful if someone could explain it or point me in the right direction. Here is the function:

$scope.filteredObject = Object.keys($scope.filterObject).reduce(function(p, collection) {
    var values = $scope.filterObject[collection];
    p[collection] = Object.keys(values).filter(function(key) {
        return values[key] === true;
    }).map(function(key) {
        return key;
    });
    return p;
}, {});

So this works great, but I'm wondering what the }, {}); at the end of the function does exactly. Im not exactly sure the name of that and googleing " }, {} after a function in javascript " seems to confuse the hell out of google (lol). Thanks!

Answer 1

• } - end of the anoymous function expression function(p, collection) { … }
• , - delimiter between multiple arguments
• {} - (empty) object literal , the second argument
• ) - end of function invocation, closing parentheses for the arguments list to .reduce(…)

Answer 2

It is an empty object and has nothing to do with the function. Have a look at the Array.prototype.reduce()

The reduce function has a second optional parameter.

arr.reduce(callback[, initialValue])

So in your case it's like this:

callback = function(p, collection) { /*...*/ };
initialValue = {}; // could also be new Object()

Hope this helps :)