There are a lot of JavaScript MVC frameworks out there. Why did we build React, and why would you want to use it?
There are a lot of JavaScript MVC frameworks out there. Why did we
build React, and why would you want to use it?
## React is not an MVC framework.
## React is not an MVC framework.
It's a library designed for building big UIs. The type where you have lots of reusable components that are handling events, presenting backend data, and accepting user input. The type where you have to integrate with legacy code, and support legacy browsers.
It's a library designed for building big UIs. The type where you have
lots of reusable components that are handling events, presenting
backend data, and accepting user input. The type where you have to
integrate with legacy code, and support legacy browsers.
In a conventional MVC application, you'd build the View with React (and maybe the Controller too, if you'd like).
In a conventional MVC application, you'd build the View with React
(and maybe the Controller too, if you'd like).
## React doesn't use templates.
## React doesn't use templates.
Traditionally, you'd create a set of templates with a template language or HTML directives to make a page dynamic. It's up to the designer of the template language or the author of the directives to provide the full set of abstractions you can use to build your front-end code.
Traditionally, you'd create a set of templates with a template
language or HTML directives to make a page dynamic. It's up to the
React's technique is to break your view down into small, composable and reusable **components**. These components provide a `render()` method which specifies how the component will generate its markup. `render()` can either return normal DOM elements (like `<div>`s) or can return other components.
designer of the template language or the author of the directives to
provide the full set of abstractions you can use to build your
This means that yes, we have JavaScript generating markup. But we think that this is an advantage over using templates for a few reasons:
front-end code.
- **JavaScript is a flexible, powerful programming language with the ability to build abstractions.** This is incredibly important in large applications.
React's technique is to break your view down into small, composable
- "Logic" and "markup" are intimately tied, and are both part of the "presentation" layer, so we're not breaking separation of concerns.
and reusable **components**. These components provide a `render()`
- Large projects usually don't use WYSIWYG editors for production code, so breaking apart markup from the code that creates it usually only introduces friction.
method which specifies how the component will generate its
- We've built a safe, convenient and fast way to compose markup and components using pure JavaScript. This means no manual string concatenation and limited surface area for XSS vulnerabilities.
markup. `render()` can either return normal DOM elements (like
`<div>`s) or can return other components.
This means that yes, we have JavaScript generating markup. But we
think that this is an advantage over using templates for a few
reasons:
- **JavaScript is a flexible, powerful programming language with the
ability to build abstractions.** This is incredibly important in
large applications.
- "Logic" and "markup" are intimately tied, and are both part of the
"presentation" layer, so we're not breaking separation of concerns.
- Large projects usually don't use WYSIWYG editors for production
code, so breaking apart markup from the code that creates it usually
only introduces friction.
- We've built a safe, convenient and fast way to compose markup and
components using pure JavaScript. This means **no manual string
concatenation** and limited surface area for XSS vulnerabilities.
## Reacting to changes
## Reacting to changes
React really shines when your data changes over time.
React really shines when your data changes over time.
In a traditional JavaScript application you need to look at what data changed and imperatively make changes to the DOM to make them consistent. Even AngularJS, which provides a declarative interface via directives and data binding, still requires a linking function to manually update DOM nodes (remember: React components are quite flexible and analogous to AngularJS directives, not templates. In big apps you'll almost certainly need this level of expressive power).
In a traditional JavaScript application you need to look at what data
changed and imperatively make changes to the DOM to make them
consistent. Even AngularJS, which provides a declarative interface via
directives and data binding, still requires a linking function to
manually update DOM nodes (remember: React components are quite
flexible and analogous to AngularJS directives, not templates. In big
apps you'll almost certainly need this level of expressive power).
React takes a different approach.
React takes a different approach.
When your component is first initialized, the `render()` method is called and a string of static HTML is inserted into the DOM. When your data changes, the `render()` method is called again. We diff the old return value from `render()` with the new one and determine the fastest way to update the DOM. So if only a single attribute on a single node has changed, that's all that React will update.
When your component is first initialized, the `render()` method is
called and a string of static HTML is inserted into the DOM. When your
We call this process **reconciliation**. Check out [this jsFiddle](http://jsfiddle.net/fv6RD/3/) for an example of reconciliation in action.
data changes, the `render()` method is called again. We diff the old
return value from `render()` with the new one and determine the
Usually reconciliation will be faster than handwritten code, as React knows about the entire state of the page and can do cool tricks like batching reads and writes and picking the fastest subset of DOM mutations to perform.
fastest way to update the DOM. So if only a single attribute on a
single node has changed, that's all that React will update.
The way we're able to pull this off is by constructing a very fast, lightweight representation of the DOM which knows which parts are dirtied and which parts are clean. That is, **the data returned from `render()` isn't a string and isn't a real DOM node, it's just a lightweight description of what the DOM should look like**.
We call this process **reconciliation**. Check out
Because this re-render is so fast (on the order of 1ms for TodoMVC), we don't need the end user to explicitly specify data bindings. We've found that this is an easy way to build apps. It's a lot like the early days of the dynamic web. Back then you wrote simple presentational code and when your data changed you simply refreshed the page. Today, React makes that "refresh" very fast and lightweight, and only changes the parts of the markup that need to be changed.
[this jsFiddle](http://jsfiddle.net/fv6RD/3/) for an example of
reconciliation in action.
No other framework we've seen can support this easily, since it would have to be built from the ground up to have very little coupling with the DOM.
Usually reconciliation will be faster than handwritten code, as React
knows about the entire state of the page and can do cool tricks like
batching reads and writes and picking the fastest subset of DOM
mutations to perform.
The way we're able to pull this off is by constructing a very fast,
lightweight representation of the DOM which knows which parts are
dirtied and which parts are clean. That is, **the data returned from
`render()` isn't a string and isn't a real DOM node, it's just a
lightweight description of what the DOM should look like**.
Because this re-render is so fast (on the order of 1ms for TodoMVC),
we don't need the end user to explicitly specify data bindings. We've
found that this is an easy way to build apps. It's a lot like the
early days of the dynamic web. Back then you wrote simple
presentational code and when your data changed you simply refreshed
the page. Today, React makes that "refresh" very fast and lightweight,
and only changes the parts of the markup that need to be changed.
No other framework we've seen can support this easily, since it would
have to be built from the ground up to have very little coupling with
the DOM.
## Not just for HTML components in the browser
## Not just for HTML components in the browser
Since React makes so few assumptions about its environment, we can do some pretty cool things with it:
Since React makes so few assumptions about its environment, we can do
some pretty cool things with it:
- Facebook.com has dynamic charts that render to `<canvas>` instead of HTML
- Instagram is a "single page" web app built entirely with React and `Backbone.Router`. Designers regularly contribute React code with JSX.
- Facebook.com has dynamic charts that render to `<canvas>` instead of
- We've built an internal prototype that runs React apps in a web worker
HTML
- You can run React [on the server](http://github.com/petehunt/react-server-rendering) for SEO, performance, code sharing and overall flexibility.
- Instagram is a "single page" web app built entirely with React and
- Events behave in a consistent, standards-compliant way in all browsers (including IE8) and automatically use [event delegation](http://davidwalsh.name/event-delegate)
`Backbone.Router`. Designers regularly contribute React code with
JSX.
Head on over to [facebook.github.io/react](http://facebook.github.io/react) to check out what we've built. Our documentation is geared towards building apps with the framework, but if you're interested in the nuts-and-bolts [get in touch](http://facebook.github.io/react/support.html) with us!
- We've built an internal prototype that runs React apps in a web
worker
- You can run React
[on the server](http://github.com/petehunt/react-server-rendering)
for SEO, performance, code sharing and overall flexibility.
- Events behave in a consistent, standards-compliant way in all
petehunt
12 years ago