How can I add an element inside a object in Javascript asking by prompt?

Question

my question is simple, how can I add a new recipe in my object asking by prompt?

var recipes =[ {name:"stuff",
               ingredients: [{name:"ingr1", weight:100}
                             {name:"ingr2", weight:150}]},
               {name:"morestuff",
                ingredients: [{name:"ingr1", weight:120}
                             {name:"ingr2", weight:180}]},
             ];