example for pi

SQUASHED: AUTO-COMMIT-src-client-reactive-polymorphic-identifiers-index.md,

Author: onsetsu

src/client/reactive/polymorphic-identifiers/index.md

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+# Polymorphic-Identifiers
+
+```JavaScript
+import { PIReference } from 'polymorphic-identifiers';
+
+// example scheme
+class qa extends PIReference {
+  read() {
+    const { elements } = this.parse();
+    return elements;
+  }
+  write(v) {
+    const { elements, type, prop } = this.parse();
+
+    if (type === 'style') {
+      return elements.forEach(e => e.style[prop] = v)
+    }
+    elements.forEach(e => e.innerHTML = v)
+  }
+
+  // helper
+  parse() {
+    const [selector, type, prop] = this.strings.first.split('/');
+    const elements = this.query(selector);
+    return { selector, type, prop, elements };
+  }
+  query(selector) {
+    return Array.from(document.querySelectorAll(selector));
+  }
+}
+
+// usage
+// calls `read`
+qa`lively-window`.forEach(lw => lively.showElement(lw))
+
+// assignments with <<
+// calls `write`
+qa`#rect` << 'html'
+qa`#rect/style/border-color` << 'green'
+```