Using Array.prototype.filter() and Array.prototype.map() I need to first filter items for an array of objects {type: 'genre', value: '123'} and after combine in a string content for property value only.

Any suggestions on how to improve the following code?

this.flattenCategories = function () {
    // flatten in a single string all categories so to be easily visaulised in the dom
    var categories = this.information.filter(function (item) {
        if (item.type === 'genre') {
            return item;
        }
    });
    this.categoriesFlatten = categories.map(function (item) {
        return item.value;
    }).join(CONFIG.app.categoriesSeparator)
},
You have a bug in your code. Filter expects true or false. Your still works because implicit type conversion of Javascript (object => true, undefined => false). 

Correct would be:

var categories = this.information.filter(function (item) {
    return item.type === 'genre';
});


Filter/Map could be combined together if you like.

You're using variable from outside. You could improve testability and readability by using of arguments and return the result.

this.flattenCategories = function (information, separator) {
    // flatten in a single string all categories so to be easily visaulised in the dom
    return information
        .filter(function (item) { return item.type === 'genre'; })
        .map(function (item) { return item.value; })
        .join(separator);
}