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!

It's .reduce(function(p, collection) { ... }, {}); In other words, the rest of the .reduce() function call. — Jared Farrish
– Jared Farrish, Commented Apr 15, 2015 at 0:38
The anonymous function and the empty object ({}) are parameters to the reduce function. — p.s.w.g
– p.s.w.g, Commented Apr 15, 2015 at 0:38

Bergi · Accepted Answer · 2015-04-15 00:38:31Z

3

} - 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(…)

answered Apr 15, 2015 at 0:38

Bergi

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Comments

tim-we · Accepted Answer · 2015-04-15 00:47:42Z

1

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 :)

answered Apr 15, 2015 at 0:47

tim-we

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