Initial version

README.md

@@ -1 +1 @@
-# tp-element
+# tp-scroll-threshold

package.json

@@ -1,14 +1,14 @@
 {
-  "name": "@tp/tp-element",
-  "version": "0.0.1",
+  "name": "@tp/tp-scroll-threshold",
+  "version": "1.0.0",
   "description": "",
-  "main": "tp-element.js",
+  "main": "tp-scroll-threshold.js",
   "scripts": {
     "test": "echo \"Error: no test specified\" && exit 1"
   },
   "repository": {
     "type": "git",
-    "url": "https://gitea.codeblob.work/tp-elements/tp-element.git"
+    "url": "https://gitea.codeblob.work/tp-elements/tp-scroll-threshold.git"
   },
   "author": "trading_peter",
   "license": "Apache-2.0",

tp-element.js

@@ -1,35 +0,0 @@
-/**
-@license
-Copyright (c) 2022 trading_peter
-This program is available under Apache License Version 2.0
-*/
-
-import { LitElement, html, css } from 'lit';
-
-class TpElement extends LitElement {
-  static get styles() {
-    return [
-      css`
-        :host {
-          display: block;
-        }
-      `
-    ];
-  }
-
-  render() {
-    const { } = this;
-
-    return html`
-
-    `;
-  }
-
-  static get properties() {
-    return { };
-  }
-
-
-}
-
-window.customElements.define('tp-element', TpElement);

tp-scroll-threshold.js

@@ -0,0 +1,99 @@
+/**
+@license
+Copyright (c) 2022 trading_peter
+This program is available under Apache License Version 2.0
+*/
+
+import { debounce } from '@tp/helpers/debounce.js';
+import { LitElement, css } from 'lit';
+
+class TpScrollThreshold extends LitElement {
+  static get styles() {
+    return [
+      css`
+        :host {
+          display: none;
+        }
+      `
+    ];
+  }
+
+  static get properties() {
+    return {
+      target: { type: Object },
+      upperThreshold: { type: Number },
+      lowerThreshold: { type: Number },
+      upperTriggered: { type: Boolean },
+      lowerTriggered: { type: Boolean },
+    };
+  }
+
+  constructor() {
+    super();
+    this.onScroll = debounce(this.onScroll.bind(this), 200);
+    this.upperThreshold = 0;
+    this.lowerThreshold = 0;
+    this.upperTriggered = false;
+    this.lowerTriggered = false;
+  }
+
+  firstUpdated() {
+    if (!this.target) {
+      console.error(this.tagname + ': Missing scroll target');
+      return
+    }
+
+    this.target.addEventListener('scroll', this.onScroll, { passive: true });
+  }
+
+  onScroll() {
+    this.checkScrollThresholds();
+  }
+
+  checkScrollThresholds() {
+    if (this.lowerTriggered && this.upperTriggered) {
+      return;
+    }
+
+    const upperScrollValue = this.horizontal ? this._scrollLeft : this._scrollTop;
+    const lowerScrollValue = this.horizontal ? this.target.scrollWidth - this._targetWidth - this._scrollLeft : this.target.scrollHeight - this._targetHeight - this._scrollTop;
+
+    // Detect upper threshold
+    if (upperScrollValue <= this.upperThreshold && !this.upperTriggered) {
+      this.upperTriggered = true;
+      this.dispatchEvent(new CustomEvent('upper-threshold', { detail: null, bubbles: true, composed: true }));
+    }
+    // Detect lower threshold
+    if (lowerScrollValue <= this.lowerThreshold && !this.lowerTriggered) {
+      this.lowerTriggered = true;
+      this.dispatchEvent(new CustomEvent('lower-threshold', { detail: null, bubbles: true, composed: true }));
+    }
+  }
+
+  clearTriggers() {
+    this.upperTriggered = false;
+    this.lowerTriggered = false;
+  }
+
+  get _doc() {
+    return this.ownerDocument.documentElement;
+  }
+
+  get _scrollTop() {
+    return this.target === this._doc ? window.pageYOffset : this.target.scrollTop;
+  }
+
+  get _scrollLeft() {
+    return this.target === this._doc ? window.pageXOffset : this.target.scrollLeft;
+  }
+
+  get _targetWidth() {
+    return this.target === this._doc ? window.innerWidth : this.target.offsetWidth;
+  }
+
+  get _targetHeight() {
+    return this.target === this._doc ? window.innerHeight : this.target.offsetHeight;
+  }
+}
+
+window.customElements.define('tp-scroll-threshold', TpScrollThreshold);