Question

I am using Backbone’s validate function to guarantee Man to have an age property more than 18. Here is my code:

var Man = Backbone.Model.extend({
    initialize : function(){
        this.on("error",function(model,error){
            alert(error);
        });
    },
    validate : function(attrs,options){
        if (attrs.age < 18){
            return 'below 18';
        } 
    }
})

var man = new Man({name : 'qian', age : 12});

But looking at the result it seems that validate doesn’t work.

Answer 1

In Backbone.js (prior to version 0.9.10), validate is called before save as well as before set.

You will get an alert error when you set invalid value.

Example – age value is below 18 :

var man = new Man ({name : 'qian', age : 12});
man.set({ age: 12 }); // that will trigger alert

EDIT

For Backbone.js version 0.9.10+ there is an issue reported: Failed validation does not trigger error callback. Issue explanation says that

invalid event should be used instead of error

So changing your code to:

var Man = Backbone.Model.extend({
    initialize : function(){
        this.on("invalid",function(model,error){
            alert(error);
        });
    },
    ...

And setting variable with validate option set to true will trigger an alert.

man.set({age: 12}, {validate : true});