gridstack · adumesny · Oct 19, 2024 · Oct 19, 2024
diff --git a/demo/index.html b/demo/index.html
@@ -15,6 +15,7 @@ <h1>Demos</h1>
     <!-- <li><a href="esmodule.html">ES Module test</a></li> -->
     <li><a href="float.html">Float grid</a></li>
     <li><a href="knockout.html">Knockout.js</a></li>
+    <li><a href="lazy_load.html">Lazy Load</a></li>
     <li><a href="mobile.html">Mobile touch</a></li>
     <li><a href="nested.html">Nested grids</a></li>
     <li><a href="nested_advanced.html">Nested Advanced grids</a></li>

diff --git a/demo/lazy_load.html b/demo/lazy_load.html
@@ -0,0 +1,36 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="utf-8">
+  <meta http-equiv="X-UA-Compatible" content="IE=edge">
+  <meta name="viewport" content="width=device-width, initial-scale=1">
+  <title>Lazy loading demo</title>
+
+  <link rel="stylesheet" href="demo.css"/>
+  <script src="../dist/gridstack-all.js"></script>
+
+</head>
+<body>
+  <div>
+    <h1>Lazy loading demo</h1>
+    <p>New V11 GridStackWidget.lazyLoad feature. open console and see widget content (or angular components) created as they become visible.</p>
+    <div style="height: 300px; overflow-y: auto">
+      <div class="grid-stack"></div>
+    </div>
+  </div>
+  <script type="text/javascript">
+    // print when widgets are created
+    GridStack.renderCB = function(el, w) {
+      el.textContent = w.content;
+      console.log('created node id ', w.id);
+    };
+    let children = [];
+    for (let y = 1; y <= 5; y++) children.push({x:0, y, id:y, content: String(y)});
+    let grid = GridStack.init({
+      cellHeight: 200,
+      children,
+      lazyLoad: true,  // delay creation until visible
+    });
+  </script>
+</body>
+</html>
diff --git a/doc/CHANGES.md b/doc/CHANGES.md
@@ -119,6 +119,7 @@ Change log
 * fix: [#2231](https://github.com/gridstack/gridstack.js/bug/2231),[#1840](https://github.com/gridstack/gridstack.js/bug/1840),[#2354](https://github.com/gridstack/gridstack.js/bug/2354)
 big overall to how we do sidepanel drag&drop helper. see release notes.
 * feat: [#2818](https://github.com/gridstack/gridstack.js/pull/2818) support for Angular Component hosting true sub-grids (that size according to parent) without requring them to be only child of grid-item-content.
+* feat: Lazy loading of widget content until visible (`GridStackOptions.lazyLoad` and `GridStackWidget.lazyLoad`)
 
 ## 10.3.1 (2024-07-21)
 * fix: [#2734](https://github.com/gridstack/gridstack.js/bug/2734) rotate() JS error

diff --git a/doc/README.md b/doc/README.md
@@ -106,6 +106,7 @@ gridstack.js API
 - `handle` - draggable handle selector (default: `'.grid-stack-item-content'`)
 - `handleClass` - draggable handle class (e.g. `'grid-stack-item-content'`). If set `handle` is ignored (default: `null`)
 - `itemClass` - widget class (default: `'grid-stack-item'`)
+- `lazyLoad?`: boolean - true when widgets are only created when they scroll into view (visible). also overridable per widget in `GridStackWidget`
 - `margin` - gap size around grid item and content (default: `10`). Can be:
   * an integer (px)
   * a string (ex: '2em', '20px', '2rem')
@@ -155,7 +156,7 @@ most of the above options are also available as HTML attributes using the `gs-`
 Extras:
 - `gs-current-row` - (internal) current rows amount. Set by the library only. Can be used by the CSS rules.
 
-## Item Options
+## Item Options - GridStackWidget
 
 options you can pass when calling `addWidget()`, `update()`, `load()` and many others
 
@@ -174,6 +175,7 @@ You need to add `noResize` and `noMove` attributes to completely lock the widget
 Note: This also allow you to set a maximum h value (but user changeable during normal resizing) to prevent unlimited content from taking too much space (get scrollbar)
 - `subGrid`?: GridStackOptions - optional nested grid options and list of children
 - `subGridDynamic`?: boolean - enable/disable the creation of sub-grids on the fly by dragging items completely over others (nest) vs partially (push). Forces `DDDragOpt.pause=true` to accomplish that.
+- `lazyLoad?`: boolean - true when widgets are only created when they scroll into view (visible). also optin on entire grid.
 
 ## Item attributes
 

diff --git a/src/gridstack.ts b/src/gridstack.ts
@@ -461,12 +461,13 @@ export class GridStack {
 
     let el: GridItemHTMLElement;
     let node: GridStackNode = w;
+    node.grid = this;
     if (node?.el) {
       el = node.el; // re-use element stored in the node
     } else if (GridStack.addRemoveCB) {
       el = GridStack.addRemoveCB(this.el, w, true, false);
     } else {
-      el = Utils.createWidgetDivs(this.opts.itemClass, w);
+      el = Utils.createWidgetDivs(this.opts.itemClass, node);
     }
 
     if (!el) return;

diff --git a/src/types.ts b/src/types.ts
@@ -191,6 +191,9 @@ export interface GridStackOptions {
   /** additional widget class (default?: 'grid-stack-item') */
   itemClass?: string;
 
+  /** true when widgets are only created when they scroll into view (visible) */
+  lazyLoad?: boolean;
+
   /**
    * gap between grid item and content (default?: 10). This will set all 4 sides and support the CSS formats below
    *  an integer (px)
@@ -331,6 +334,8 @@ export interface GridStackWidget extends GridStackPosition {
   id?: string;
   /** html to append inside as content */
   content?: string;
+  /** true when widgets are only created when they scroll into view (visible) */
+  lazyLoad?: boolean;
   /** local (vs grid) override - see GridStackOptions.
    * Note: This also allow you to set a maximum h value (but user changeable during normal resizing) to prevent unlimited content from taking too much space (get scrollbar) */
   sizeToContent?: boolean | number;
@@ -447,4 +452,6 @@ export interface GridStackNode extends GridStackWidget {
   _removeDOM?: boolean;
   /** @internal had drag&drop been initialized */
   _initDD?: boolean;
+  /** @internal  allow delay creation when visible */
+  _visibleObservable?: IntersectionObserver;
 }
diff --git a/src/utils.ts b/src/utils.ts
@@ -110,19 +110,29 @@ export class Utils {
     return els;
   }
 
-  /** create the default grid item divs */
-  static createWidgetDivs(itemClass?: string, w?: GridStackWidget): HTMLElement {
+  /** create the default grid item divs, and content possibly lazy loaded calling GridStack.renderCB */
+  static createWidgetDivs(itemClass: string, n: GridStackNode): HTMLElement {
     const el = Utils.createDiv(['grid-stack-item', itemClass]);
-    Utils.createDiv(['grid-stack-item-content'], el, w);
+    const cont = Utils.createDiv(['grid-stack-item-content'], el);
+
+    const lazyLoad = n.lazyLoad || n.grid?.opts?.lazyLoad && n.lazyLoad !== false;
+    if (lazyLoad) {
+      n._visibleObservable = new IntersectionObserver(([entry]) => { if (entry.isIntersecting) {
+        n._visibleObservable.disconnect();
+        delete n._visibleObservable;
+        GridStack.renderCB(cont, n)
+      }});
+      window.setTimeout(() => n._visibleObservable.observe(el)); // wait until callee sets position attributes
+    } else GridStack.renderCB(cont, n);
+
     return el;
   }
 
-  /** create a div (possibly 2) with the given classes */
-  static createDiv(classes: string[], parent?: HTMLElement, w?: GridStackWidget): HTMLElement {
+  /** create a div with the given classes */
+  static createDiv(classes: string[], parent?: HTMLElement): HTMLElement {
     const el = document.createElement('div');
     classes.forEach(c => {if (c) el.classList.add(c)});
     parent?.appendChild(el);
-    if (w) GridStack.renderCB(el, w);
     return el;
   }