code improvements, fix errors

svg-sparkline.js

@@ -64,6 +64,10 @@ class SVGSparkline extends HTMLElement {
  }
 
  render() {
+ if (!this.hasAttribute("values")) {
+ return
+ }
+
  this.values = this.getAttribute("values").split(",")
  this.width = parseFloat(this.getAttribute("width")) || 160
  this.height = parseFloat(this.getAttribute("height")) || 28
@@ -135,25 +139,27 @@ class SVGSparkline extends HTMLElement {
  }
 
  initTemplate() {
- let template = document.createElement("template")
- template.innerHTML = this.render()
- this.shadowRoot.appendChild(template.content.cloneNode(true))
- }
+ if (this.shadowRoot) {
+  this.shadowRoot.innerHTML = this.render()
+  return
+  }
 
- init() {
- this.attachShadow({
- mode: "open"
- });
+ let shadowroot = this.attachShadow({ mode: "open" });
 
  let sheet = new CSSStyleSheet();
- sheet.replace(SVGSparkline.css);
- this.shadowRoot.adoptedStyleSheets = [sheet];
+ sheet.replaceSync(SVGSparkline.css);
+ shadowroot.adoptedStyleSheets = [sheet];
+
+ let template = document.createElement("template")
+ template.innerHTML = this.render()
+ shadowroot.appendChild(template.content.cloneNode(true))
+ }
 
+ async init() {
  this.initTemplate()
  }
 
- attributeChangedCallback(name, oldValue, newValue) {
- this.shadowRoot.innerHTML = ``
+ attributeChangedCallback() {
  this.initTemplate()
  }