extract the ID field using extractField

This makes the ID field extraction consistent with other fields, making
it possible to customize the extraction logic.

_Note_: a test case that was asserting a special behavior for the ID
field extraction when it matches a default object property name (like
"constructor") was removed. It's better to let the user specify their
own extractField function instead of second guessing them. This is not
considered to be a breaking change, as the existing behavior was not
publicly documented, and would only take place in corner cases (when the
idField is set to a default object property name like "constructor",
which should be discouraged anyway).

src/MiniSearch.js

@@ -180,10 +180,11 @@ class MiniSearch {
   */
   add (document) {
     const { extractField, tokenize, processTerm, fields, idField } = this._options
-    if (getOwnProperty(document, idField) == null) {
+    const id = extractField(document, idField)
+    if (id == null) {
       throw new Error(`MiniSearch: document does not have ID field "${idField}"`)
     }
-    const shortDocumentId = addDocumentId(this, document[idField])
+    const shortDocumentId = addDocumentId(this, id)
     saveStoredFields(this, shortDocumentId, document)
 
     fields.forEach(field => {
@@ -253,16 +254,17 @@ class MiniSearch {
   */
   remove (document) {
     const { tokenize, processTerm, extractField, fields, idField } = this._options
+    const id = extractField(document, idField)
 
-    if (getOwnProperty(document, idField) == null) {
+    if (id == null) {
       throw new Error(`MiniSearch: document does not have ID field "${idField}"`)
     }
 
     const [shortDocumentId] = Object.entries(this._documentIds)
-      .find(([_, longId]) => document[idField] === longId) || []
+      .find(([_, longId]) => id === longId) || []
 
     if (shortDocumentId == null) {
-      throw new Error(`MiniSearch: cannot remove document with ID ${document[idField]}: it is not in the index`)
+      throw new Error(`MiniSearch: cannot remove document with ID ${id}: it is not in the index`)
     }
 
     fields.filter(field => getOwnProperty(document, field) != null).forEach(field => {

src/MiniSearch.test.js

@@ -40,11 +40,17 @@ describe('MiniSearch', () => {
       }).toThrowError('MiniSearch: document does not have ID field "foo"')
     })
 
-    it('throws error if the document does not have the ID field, even when named like a default object property', () => {
-      const ms = new MiniSearch({ idField: 'constructor', fields: ['title', 'text'] })
-      expect(() => {
-        ms.add({ text: 'I do not have an ID' })
-      }).toThrowError('MiniSearch: document does not have ID field "constructor"')
+    it('extracts the ID field using extractField', () => {
+      const extractField = (document, fieldName) => {
+        if (fieldName === 'id') { return document['id']['value'] }
+        return MiniSearch.getDefault('extractField')(document, fieldName)
+      }
+      const ms = new MiniSearch({ fields: ['text'], extractField })
+
+      ms.add({ id: { value: 123 }, text: 'Nel mezzo del cammin di nostra vita' })
+
+      const results = ms.search('vita')
+      expect(results[0].id).toEqual(123)
     })
 
     it('rejects falsy terms', () => {
@@ -181,13 +187,6 @@ describe('MiniSearch', () => {
       }).toThrowError('MiniSearch: document does not have ID field "foo"')
     })
 
-    it('throws error if the document does not have the ID field, even if named like a default property of object', () => {
-      const ms = new MiniSearch({ idField: 'constructor', fields: ['title', 'text'] })
-      expect(() => {
-        ms.remove({ text: 'I do not have an ID' })
-      }).toThrowError('MiniSearch: document does not have ID field "constructor"')
-    })
-
     it('does not crash when the document has field named like default properties of object', () => {
       const ms = new MiniSearch({ fields: ['constructor'] })
       const document = { id: 1 }