feat: Unified highlighting (#206)

The unified highlighter is only supported in elasticsearch 6.0 and later.

Author: chrinor2002

src/core/highlight.js

@@ -19,7 +19,7 @@ const invalidEncoderParam = invalidParam(
 const invalidTypeParam = invalidParam(
     ES_REF_URL,
     'type',
-    "'plain', 'postings' or 'fvh'"
+    "'plain', 'postings', 'unified' or 'fvh'"
 );
 const invalidFragmenterParam = invalidParam(
     ES_REF_URL,
@@ -449,13 +449,16 @@ class Highlight {
      * The `unified` highlighter outputs the same highlighting when
      * `index_options` is set to `offsets`.
      *
+     * Note: The `unified` highlighter is only supported in elasticsearch 6.0
+     * and later.
+     *
      * @example
      * const highlight = esb.highlight('content').type('plain', 'content');
      *
-     * @param {string} type The allowed values are: `plain`, `postings` and `fvh`.
+     * @param {string} type The allowed values are: `plain`, `postings`, `unified` and `fvh`.
      * @param {string=} field An optional field name
      * @returns {Highlight} returns `this` so that calls can be chained
-     * @throws {Error} Type can be one of `plain`, `postings` or `fvh`.
+     * @throws {Error} Type can be one of `plain`, `postings`, `unified` or `fvh`.
      */
     type(type, field) {
         if (isNil(type)) invalidTypeParam(type);
@@ -464,6 +467,7 @@ class Highlight {
         if (
             typeLower !== 'plain' &&
             typeLower !== 'postings' &&
+            typeLower !== 'unified' &&
             typeLower !== 'fvh'
         ) {
             invalidTypeParam(type);

src/index.d.ts

@@ -8932,11 +8932,11 @@ declare namespace esb {
          * Note: The `postings` highlighter has been removed in elasticsearch 6.0. The `unified`
          * highlighter outputs the same highlighting when `index_options` is set to `offsets`.
          *
-         * @param {string} type The allowed values are: `plain`, `postings` and `fvh`.
+         * @param {string} type The allowed values are: `plain`, `postings`, `unified` and `fvh`.
          * @param {string=} field An optional field name
-         * @throws {Error} Type can be one of `plain`, `postings` or `fvh`.
+         * @throws {Error} Type can be one of `plain`, `postings`, `unified` or `fvh`.
          */
-        type(type: 'plain' | 'postings' | 'fvh', field?: string): this;
+        type(type: 'plain' | 'postings' | 'unified' | 'fvh', field?: string): this;
 
         /**
          * Forces the highlighting to highlight fields based on the source

test/core-test/highlight.test.js

@@ -106,7 +106,12 @@ test(illegalParamType, new Highlight(), 'fields', 'Array');
 test(illegalParamType, new Highlight(), 'highlightQuery', 'Query');
 test(illegalParamType, new Highlight(), 'matchedFields', 'Array');
 test(validatedCorrectly, highlight, 'encoder', ['default', 'html']);
-test(validatedCorrectly, highlight, 'type', ['plain', 'postings', 'fvh']);
+test(validatedCorrectly, highlight, 'type', [
+    'plain',
+    'postings',
+    'unified',
+    'fvh'
+]);
 test(validatedCorrectly, highlight, 'fragmenter', ['simple', 'span']);
 test(setHighlightOption, 'preTags', ['<tag1>', '<tag2>']);
 test('sets pre_tags(str) option', setHighlightOption, 'preTags', '<tag1>', [