blog.stevanfreeborn.com/src/Blog/wwwroot/Blog.lib.module.js

const pageScriptInfoBySrc = new Map();

function registerPageScriptElement(src) {
  if (!src) {
    throw new Error('Must provide a non-empty value for the "src" attribute.');
  }

  let pageScriptInfo = pageScriptInfoBySrc.get(src);

  if (pageScriptInfo) {
    pageScriptInfo.referenceCount++;
    return;
  }

  pageScriptInfo = { referenceCount: 1, module: null };
  pageScriptInfoBySrc.set(src, pageScriptInfo);
  initializePageScriptModule(src, pageScriptInfo);
}

function unregisterPageScriptElement(src) {
  if (!src) {
    return;
  }

  const pageScriptInfo = pageScriptInfoBySrc.get(src);
  
  if (!pageScriptInfo) {
    return;
  }

  pageScriptInfo.referenceCount--;
}

async function initializePageScriptModule(src, pageScriptInfo) {
  // If the path is relative, normalize it by by making it an absolute URL
  // with document's the base HREF.
  if (src.startsWith("./")) {
    src = new URL(src.substr(2), document.baseURI).toString();
  }

  const module = await import(src);

  if (pageScriptInfo.referenceCount <= 0) {
    // All page-script elements with the same 'src' were
    // unregistered while we were loading the module.
    return;
  }

  pageScriptInfo.module = module;
  module.onLoad?.();
  module.onUpdate?.();
}

function onEnhancedLoad() {
  // Start by invoking 'onDispose' on any modules that are no longer referenced.
  for (const [src, { module, referenceCount }] of pageScriptInfoBySrc) {
    if (referenceCount <= 0) {
      module?.onDispose?.();
      pageScriptInfoBySrc.delete(src);
    }
  }

  // Then invoke 'onUpdate' on the remaining modules.
  for (const { module } of pageScriptInfoBySrc.values()) {
    module?.onUpdate?.();
  }
}

export function afterWebStarted(blazor) {
  customElements.define(
    "page-script",
    class extends HTMLElement {
      static observedAttributes = ["src"];

      // We use attributeChangedCallback instead of connectedCallback
      // because a page-script element might get reused between enhanced
      // navigations.
      attributeChangedCallback(name, oldValue, newValue) {
        if (name !== "src") {
          return;
        }

        this.src = newValue;
        unregisterPageScriptElement(oldValue);
        registerPageScriptElement(newValue);
      }

      disconnectedCallback() {
        unregisterPageScriptElement(this.src);
      }
    }
  );

  blazor.addEventListener("enhancedload", onEnhancedLoad);
}