main.js

// Version 1
var view = new view({
    initialize: function () {
        this.html(this.template({}));
        this.partview = new PartView({
            el: this.$('.class-part1')
        });
        this.partview2 = new PartView({
            el: this.$('.class-part2')
        });
    },
    render: function () {
        this.partview.render();
        this.partview.render2();
    }
});

// Version 2
var view = new view({
    initialize: function () {
    },
    render: function () {
        this.html(this.template({}));
        this.partview = new PartView({
            el: this.$('.class-part1')
        });
        this.partview.render(); // Optionally, each partview renders on initialize
        this.partview2 = new PartView({
            el: this.$('.class-part2')
        });
        this.partview.render2();
    }
});

// Version 3
var view = new view({
    initialize: function () {
    },
    render: function () {
        this.html(this.template({}));
        this.partview = new PartView({
        });
        this.$('.class-part1').html(this.partview.el);
        this.partview2 = new PartView({
            el: this.$('.class-part2')
        });
        this.$('.class-part2').html(this.partview2.el);

        // Assuming each partview renders itself on initialize.
    }
});