feat(aio): add attribute utils for code atty interpretation.

These utils support flexible, natural attribute interpretation as applied to code-example and code-pane. Then apply those utils to code-example and live-example

aio/src/app/shared/attribute-utils.ts

@@ -0,0 +1,48 @@
+// Utilities for processing HTML element attributes
+import { ElementRef } from '@angular/core';
+
+interface StringMap { [index: string]: string; }
+
+/**
+ * Get attribute map from element or ElementRef `attributes`.
+ * Attribute map keys are forced lowercase for case-insensitive lookup.
+ * @param el The source of the attributes
+ */
+export function getAttrs(el:  HTMLElement | ElementRef): StringMap {
+  const attrs: NamedNodeMap = el instanceof ElementRef ? el.nativeElement.attributes : el.attributes;
+  const attrMap = {};
+  Object.keys(attrs).forEach(key =>
+    attrMap[(attrs[key] as Attr).name.toLowerCase()] = (attrs[key] as Attr).value);
+  return attrMap;
+}
+
+/**
+ * Return the attribute that matches `atty`.
+ * @param atty Name of the attribute or a string of candidate attribute names
+ */
+export function getAttrValue(attrs: StringMap, attr: string | string[] = ''): string {
+  return attrs[typeof attr === 'string' ? attr : attr.find(a => attrs[a] !== undefined)];
+}
+
+/**
+ * Return the boolean state of an attribute value (if supplied)
+ * @param attyValue The string value of some attribute (or undefined if attribute not present)
+ * @param def Default boolean value when attribute is undefined.
+ */
+export function boolFromValue(attrValue: string, def: boolean = false) {
+  // tslint:disable-next-line:triple-equals
+  return attrValue == undefined ? def :  attrValue.trim() !== 'false';
+}
+
+/**
+ * Return the boolean state of attribute from an element
+ * @param el The source of the attributes
+ * @param atty Name of the attribute or a string of candidate attribute names
+ * @param def Default boolean value when attribute is undefined.
+ */
+export function getBoolFromAttribute(
+  el:  HTMLElement | ElementRef,
+  attr: string | string[],
+  def: boolean = false): boolean {
+  return boolFromValue(getAttrValue(getAttrs(el), attr), def);
+}