refactor(aio): clean up attribute-utils (#23960)

PR Close #23960

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

@@ -1,6 +1,6 @@
 import { ElementRef } from '@angular/core';
 
-import { getAttrs, getAttrValue, getBoolFromAttribute, boolFromValue } from './attribute-utils';
+import { AttrMap, getAttrs, getAttrValue, getBoolFromAttribute, boolFromValue } from './attribute-utils';
 
 describe('Attribute Utilities', () => {
   let testEl: HTMLElement;
@@ -32,17 +32,17 @@ describe('Attribute Utilities', () => {
   });
 
   describe('getAttrValue', () => {
-    let attrMap: { [index: string]: string };
+    let attrMap: AttrMap;
 
     beforeEach(() => {
       attrMap = getAttrs(testEl);
     });
 
-    it('should return empty string value for attribute "a"', () => {
+    it('should return empty string for attribute "a"', () => {
       expect(getAttrValue(attrMap, 'a')).toBe('');
     });
 
-    it('should return empty string value for attribute "A"', () => {
+    it('should return empty string for attribute "A"', () => {
       expect(getAttrValue(attrMap, 'A')).toBe('');
     });
 
@@ -50,7 +50,7 @@ describe('Attribute Utilities', () => {
       expect(getAttrValue(attrMap, 'b')).toBe('true');
     });
 
-    it('should return empty string value for attribute "d-E"', () => {
+    it('should return empty string for attribute "d-E"', () => {
       expect(getAttrValue(attrMap, 'd-E')).toBe('');
     });
 
@@ -68,12 +68,10 @@ describe('Attribute Utilities', () => {
       expect(getAttrValue(attrMap, ['d-e', 'd'])).toBe('');
     });
 
-    it('should return undefined value for non-existent attribute "x"', () => {
+    it('should return undefined for non-existent attributes', () => {
       expect(getAttrValue(attrMap, 'x')).toBeUndefined();
-    });
+      expect(getAttrValue(attrMap, '')).toBeUndefined();
-
+      expect(getAttrValue(attrMap, ['', 'x'])).toBeUndefined();
-    it('should return undefined if no argument', () => {
-      expect(getAttrValue(attrMap)).toBeUndefined();
     });
 
   });

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

@@ -1,17 +1,19 @@
 // Utilities for processing HTML element attributes
 import { ElementRef } from '@angular/core';
 
-interface StringMap { [index: string]: string; }
+export interface AttrMap {
+  [key: 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
+ * @param el The source of the attributes.
  */
-export function getAttrs(el:  HTMLElement | ElementRef): StringMap {
+export function getAttrs(el:  HTMLElement | ElementRef): AttrMap {
   const attrs: NamedNodeMap = el instanceof ElementRef ? el.nativeElement.attributes : el.attributes;
-  const attrMap: StringMap = {};
+  const attrMap: AttrMap = {};
-  for (const attr of attrs as any /* cast due to https://github.com/Microsoft/TypeScript/issues/2695 */) {
+  for (const attr of attrs as any as Attr[] /* cast due to https://github.com/Microsoft/TypeScript/issues/2695 */) {
     attrMap[attr.name.toLowerCase()] = attr.value;
   }
   return attrMap;
@@ -19,29 +21,29 @@ export function getAttrs(el:  HTMLElement | ElementRef): StringMap {
 
 /**
  * Return the attribute that matches `attr`.
- * @param attr Name of the attribute or a string of candidate attribute names
+ * @param attr Name of the attribute or a string of candidate attribute names.
  */
-export function getAttrValue(attrs: StringMap, attr: string | string[] = ''): string {
+export function getAttrValue(attrs: AttrMap, attr: string | string[]): string | undefined {
-  return attrs[typeof attr === 'string' ?
+  const key = (typeof attr === 'string')
-    attr.toLowerCase() :
+      ? attr
-    attr.find(a => attrs[a.toLowerCase()] !== undefined) || ''
+      : attr.find(a => attrs.hasOwnProperty(a.toLowerCase()));
-  ];
+
+  return (key === undefined) ? undefined : attrs[key.toLowerCase()];
 }
 
 /**
  * Return the boolean state of an attribute value (if supplied)
- * @param attrValue The string value of some attribute (or undefined if attribute not present)
+ * @param attrValue 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|undefined, def: boolean = false) {
+export function boolFromValue(attrValue: string | undefined, def: boolean = false) {
-  // tslint:disable-next-line:triple-equals
+  return attrValue === undefined ? def : attrValue.trim() !== 'false';
-  return attrValue == undefined ? def :  attrValue.trim() !== 'false';
 }
 
 /**
  * Return the boolean state of attribute from an element
- * @param el The source of the attributes
+ * @param el The source of the attributes.
- * @param atty Name of the attribute or a string of candidate attribute names
+ * @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(