What is the best Javascript web framework to use to build a single page web app?
There are several popular JavaScript frameworks that can be used to build single-page web applications. The choice of framework largely depends on your specific needs and preferences, as each framework has its own strengths and weaknesses. Here are some popular JavaScript frameworks for building single-page web apps:

1. React.js: Developed by Facebook, React.js is one of the most popular JavaScript frameworks for building single-page web applications. It is known for its component-based architecture, which allows for easy reusability of code and efficient rendering of UI components.

1. AngularJS: Developed by Google, AngularJS is another popular framework for building single-page web applications. It provides features such as two-way data binding, dependency injection, and directives, making it a powerful tool for building complex web applications.

1. Vue.js: Vue.js is a relatively new JavaScript framework that has gained popularity in recent years. It is known for its simplicity and ease of use, and provides features such as a reactive data binding system and a virtual DOM.

1. Ember.js: Ember.js is a powerful JavaScript framework that provides features such as data binding, routing, and templates. It is known for its convention-over-configuration approach and is well-suited for building large-scale applications.

1. Backbone.js: Backbone.js is a lightweight JavaScript framework that provides a basic set of features for building single-page web applications. It is known for its flexibility and ease of use.

Each of these frameworks has its own set of features and benefits, so it's important to choose the one that best fits your specific needs and preferences.