From ce6d89bc5c408d9458add5157a6ab963669f79b7 Mon Sep 17 00:00:00 2001
From: Andrew Kingston <aptkingston@ssl-mail.com>
Date: Thu, 21 Jan 2021 10:41:30 +0000
Subject: [PATCH] Only update components when their props actually change

---
 packages/client/src/components/Component.svelte | 17 +++++++++++++++--
 packages/client/src/utils/componentProps.js     | 16 ++++++++++++++++
 2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/packages/client/src/components/Component.svelte b/packages/client/src/components/Component.svelte
index 322d083f94..ffa6b38c43 100644
--- a/packages/client/src/components/Component.svelte
+++ b/packages/client/src/components/Component.svelte
@@ -3,10 +3,11 @@
   import { writable } from "svelte/store"
   import * as ComponentLibrary from "@budibase/standard-components"
   import Router from "./Router.svelte"
-  import { enrichProps } from "../utils/componentProps"
+  import { enrichProps, propsAreSame } from "../utils/componentProps"
   import { bindingStore, builderStore } from "../store"
 
   export let definition = {}
+  let componentProps = {}
 
   // Get contexts
   const dataContext = getContext("data")
@@ -21,6 +22,7 @@
   $: children = definition._children
   $: id = definition._id
   $: enrichedProps = enrichProps(definition, $dataContext, $bindingStore)
+  $: updateProps(enrichedProps)
   $: styles = definition._styles
 
   // Allow component selection in the builder preview if we're previewing a
@@ -31,6 +33,17 @@
   // Update component context
   $: componentStore.set({ id, styles: { ...styles, id, allowSelection } })
 
+  // Updates the component props.
+  // Most props are deeply compared so that svelte will only trigger reactive
+  // statements on props that have actually changed.
+  const updateProps = props => {
+    Object.keys(props).forEach(key => {
+      if (!propsAreSame(props[key], componentProps[key])) {
+        componentProps[key] = props[key]
+      }
+    })
+  }
+
   // Gets the component constructor for the specified component
   const getComponentConstructor = component => {
     const split = component?.split("/")
@@ -51,7 +64,7 @@
 </script>
 
 {#if constructor}
-  <svelte:component this={constructor} {...enrichedProps}>
+  <svelte:component this={constructor} {...componentProps}>
     {#if children && children.length}
       {#each children as child (getChildKey(child._id))}
         <svelte:self definition={child} />
diff --git a/packages/client/src/utils/componentProps.js b/packages/client/src/utils/componentProps.js
index be65ad2bfe..c5dffe4336 100644
--- a/packages/client/src/utils/componentProps.js
+++ b/packages/client/src/utils/componentProps.js
@@ -1,6 +1,22 @@
 import { enrichDataBindings } from "./enrichDataBinding"
 import { enrichButtonActions } from "./buttonActions"
 
+/**
+ * Deeply compares 2 props using JSON.stringify.
+ * Does not consider functions, as currently only button actions have a function
+ * prop and it's cheaper to just always re-render buttons than it is to deeply
+ * compare them.
+ */
+export const propsAreSame = (a, b) => {
+  if (a === b) {
+    return true
+  }
+  if (typeof a === "function" || typeof b === "function") {
+    return false
+  }
+  return JSON.stringify(a) === JSON.stringify(b)
+}
+
 /**
  * Enriches component props.
  * Data bindings are enriched, and button actions are enriched.