use Object.defineProperty to do data-binding

data-binding.js

var formInputValue = '[email protected]';

var model = {};
Object.defineProperty(model, 'email', {
    get: function () {
        return formInputValue;
    },
    set: function (value) {
        console.log(value);
        formInputValue = value;
    }
});

console.assert(model.email === formInputValue);
model.email = '[email protected]';
console.assert(formInputValue === '[email protected]');

about IE browser support, see https://msdn.microsoft.com/zh-cn/library/dd548687(v=vs.94).aspx

ViewModel