Converting callbacks to promises

file.js

//Backbone.Model's save function is a function that takes callbacks
//for successful or failed saves.  

//Normal usage

let model = new Backbone.Model();

model.save(null, {
    success: function() {
        alert('saved');
    },
    error: function() {
        alert('failed to save');
    }
});

//We can create a save function that takes a model and returns a Promise

function save(model) {
    return new Promise(function(resolve, reject) {
        model.save(null, {
            success: resolve,
            error: reject,
        })
    })
}

//new usage

save(model).then(function() {
    alert('saved');
}).catch(function() {
    alert('failed to save');
})