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add note about synchronicity

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Leo Horie 2016-11-15 10:16:01 -05:00
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docs/render.md
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@ -1,7 +1,8 @@
# render(element, vnodes)
- [API](#api)
- [How it works](#how it works)
- [How it works](#how-it-works)
- [Why Virtual DOM](#why-virtual-dom)
- [Differences from other API methods](#differences-from-other-api-methods)
- [Standalone usage](#standalone-usage)
@ -23,7 +24,13 @@ Argument | Type | Required | Description
### How it works
The `m.render(element, vnodes)` method takes a virtual DOM tree (typically generated via the [`m()` hyperscript function](hyperscript.md), generates a DOM tree and mounts it on `element`. If `element` already has a DOM tree mounted via a previous `m.render()` call, `vnodes` is diffed against the previous `vnodes` tree and the existing DOM tree is modified only where needed to reflect the changes. Unchanged DOM nodes are not touched at all.
The `m.render(element, vnodes)` method takes a virtual DOM tree (typically generated via the [`m()` hyperscript function](hyperscript.md), generates a DOM tree and mounts it on `element`. If `element` already has a DOM tree mounted via a previous `m.render()` call, `vnodes` is diffed against the previous `vnodes` tree and the existing DOM tree is modified only where needed to reflect the changes. Unchanged DOM nodes are not touched at all.
`m.render` is synchronous.
---
### Why Virtual DOM
It may seem wasteful to generate a vnode tree on every redraw, but as it turns out, creating and comparing Javascript data structures is surprisingly cheap compared to reading and modifying the DOM.