feat: add memorization interface

src/memo.ts

@@ -0,0 +1,43 @@
+import {
+  CssSelectors,
+  CssSelectorsByType,
+  CssSelectorType,
+  CssSelectorTypes
+} from './types';
+import {SELECTOR_TYPE_GETTERS} from './utilities-selectors';
+
+type MemoSelectorData = Map<CssSelectorType, CssSelectors>
+type MemoElementData = Map<Element, MemoSelectorData>
+
+/**
+ * Creates interface for getting CSS selectors by type for an element. Results are remembered for use in later calls.
+ */
+export function createMemo (memo: MemoElementData = new Map()) {
+
+  function getElementData (element: Element): MemoSelectorData {
+    if (!memo.get(element)) {
+      memo.set(element, new Map());
+    }
+    return memo.get(element);
+  }
+
+  function getSelectorData (element: Element, selectorType: CssSelectorType) {
+    const elementData = getElementData(element);
+    if (!elementData.get(selectorType)) {
+      elementData.set(selectorType, getSelectors(element, selectorType));
+    }
+    return elementData.get(selectorType);
+  }
+
+  function getSelectors (element: Element, selectorType: CssSelectorType): CssSelectors {
+    return SELECTOR_TYPE_GETTERS[selectorType](element);
+  }
+
+  return function (element: Element, selectors: CssSelectorTypes): CssSelectorsByType {
+    const result = {} as CssSelectorsByType;
+    selectors.forEach((selectorType) => {
+      result[selectorType] = getSelectorData(element, selectorType);
+    });
+    return result;
+  };
+}

src/types.ts

@@ -1,10 +1,14 @@
 import {VALID_SELECTOR_TYPES} from './constants'
 
 export type CssSelector = string
+export type CssSelectors = Array<CssSelector>
 
 export type CssSelectorMatch = RegExp | string
 
 export type CssSelectorType = typeof VALID_SELECTOR_TYPES[number]
+export type CssSelectorTypes = Array<CssSelectorType>
+
+export type CssSelectorsByType = Record<CssSelectorType, CssSelectors>
 
 export type CssSelectorData = {
   [key in CssSelectorType]?: Array<string> | Array<Array<string>>

test/memo.spec.js

@@ -0,0 +1,47 @@
+import {assert} from 'chai'
+import {createMemo} from '../src/memo'
+
+describe('memo', () => {
+
+  let root
+
+  /**
+   * Simple way to retrieve target element for test.
+   * @returns {Element}
+   */
+  function getTargetElement () {
+    return root.querySelector('[data-target]')
+  }
+
+  beforeEach(() => {
+    root = document.body.appendChild(document.createElement('div'))
+  })
+
+  afterEach(() => {
+    root.parentNode.removeChild(root)
+  })
+
+  it('should retrieve selectors for an element', () => {
+    root.innerHTML = '<div data-target></div>'
+    const element = getTargetElement()
+    const getElementSelectors = createMemo()
+    const result = getElementSelectors(element, ['tag'])
+    assert.deepEqual(result, {tag: ['div']})
+  })
+
+  it('should use remembered value', () => {
+    root.innerHTML = '<div data-target></div>'
+    const element = getTargetElement()
+    const memoData = new Map([
+      [
+        element,
+        new Map([
+          ['tag', ['mock_tag_selector']]
+        ])
+      ]
+    ])
+    const getElementSelectors = createMemo(memoData)
+    const result = getElementSelectors(element, ['tag'])
+    assert.deepEqual(result, {tag: ['mock_tag_selector']})
+  })
+})