[preact] Optimize performance of prop bindings #153
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marvinhagemeister
approved these changes
Sep 15, 2022
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In Preact 10, new
VNodeinstances are passed to theDIFFhook on every render. In the previous prop bindings implementation, this was causing signal prop values to be bound on every VDOM render, leaking memory and doing unnecessary work.This new approach replaces Signal prop values with their peek()'d current values in order to allow Preact to render those props using its standard setProperty mechanics, and the Signal instances are stored in a new property attached to the element VNode. After a VNode is diffed (
options.diffed), if it has Signals stored in this new property, their DOM bindings are set up using an Updater that is stored on the DOM element itself - this works because DOM elements are stable references in Preact 10, whereas VNodes are not.The implementation in this PR uses a single Updater instance for each Element VNode with one or more Signal prop values. Any time one of the Signals is changed, the Updater loops over the current set of Signals bound to its associated element and compares their new value to a cached copy - if the value is different, a DOM mutation is performed. In the future when #136 has landed, it may be more efficient (and smaller) to instead do per-signal-prop bindings using Effect. I have a version locally that does this.