Add support for tooltip offset option to be a function

js/src/tooltip.js

@@ -32,7 +32,7 @@ const DefaultType = {
   html              : 'boolean',
   selector          : '(string|boolean)',
   placement         : '(string|function)',
-  offset            : '(number|string)',
+  offset            : '(number|string|function)',
   container         : '(string|element|boolean)',
   fallbackPlacement : '(string|array)',
   boundary          : '(string|element)'
@@ -285,9 +285,7 @@ class Tooltip {
       this._popper = new Popper(this.element, tip, {
         placement: attachment,
         modifiers: {
-          offset: {
-            offset: this.config.offset
-          },
+          offset: this._getOffset(),
           flip: {
             behavior: this.config.fallbackPlacement
           },
@@ -450,6 +448,25 @@ class Tooltip {
 
   // Private
 
+  _getOffset() {
+    const offset = {}
+
+    if (typeof this.config.offset === 'function') {
+      offset.fn = (data) => {
+        data.offsets = {
+          ...data.offsets,
+          ...this.config.offset(data.offsets, this.element) || {}
+        }
+
+        return data
+      }
+    } else {
+      offset.offset = this.config.offset
+    }
+
+    return offset
+  }
+
   _getContainer() {
     if (this.config.container === false) {
       return document.body

js/tests/unit/tooltip.js

@@ -1069,4 +1069,41 @@ $(function () {
 
     assert.strictEqual(tooltip._isEnabled, true)
   })
+
+  QUnit.test('should create offset modifier correctly when offset option is a function', function (assert) {
+    assert.expect(2)
+
+    var getOffset = function (offsets) {
+      return offsets
+    }
+
+    var $trigger = $('<a href="#" rel="tooltip" data-trigger="click" title="Another tooltip"/>')
+      .appendTo('#qunit-fixture')
+      .bootstrapTooltip({
+        offset: getOffset
+      })
+
+    var tooltip = $trigger.data('bs.tooltip')
+    var offset = tooltip._getOffset()
+
+    assert.ok(typeof offset.offset === 'undefined')
+    assert.ok(typeof offset.fn === 'function')
+  })
+
+  QUnit.test('should create offset modifier correctly when offset option is not a function', function (assert) {
+    assert.expect(2)
+
+    var myOffset = 42
+    var $trigger = $('<a href="#" rel="tooltip" data-trigger="click" title="Another tooltip"/>')
+      .appendTo('#qunit-fixture')
+      .bootstrapTooltip({
+        offset: myOffset
+      })
+
+    var tooltip = $trigger.data('bs.tooltip')
+    var offset = tooltip._getOffset()
+
+    assert.strictEqual(offset.offset, myOffset)
+    assert.ok(typeof offset.fn === 'undefined')
+  })
 })

package.json

@@ -186,11 +186,11 @@
     },
     {
       "path": "./dist/js/bootstrap.bundle.min.js",
-      "maxSize": "21 kB"
+      "maxSize": "21.25 kB"
     },
     {
       "path": "./dist/js/bootstrap.js",
-      "maxSize": "22.5 kB"
+      "maxSize": "23 kB"
     },
     {
       "path": "./dist/js/bootstrap.min.js",

site/docs/4.2/components/tooltips.md

@@ -234,9 +234,13 @@ Options can be passed via data attributes or JavaScript. For data attributes, ap
     </tr>
     <tr>
       <td>offset</td>
-      <td>number | string</td>
+      <td>number | string | function</td>
       <td>0</td>
-      <td>Offset of the tooltip relative to its target. For more information refer to Popper.js's <a href="https://popper.js.org/popper-documentation.html#modifiers..offset.offset">offset docs</a>.</td>
+      <td>
+        <p>Offset of the tooltip relative to its target.</p>
+        <p>When a function is used to determine the offset, it is called with an object containing the offset data as its first argument. The function must return an object with the same structure. The triggering element DOM node is passed as the second argument.</p>
+        <p>For more information refer to Popper.js's <a href="https://popper.js.org/popper-documentation.html#modifiers..offset.offset">offset docs</a>.</p>
+      </td>
     </tr>
     <tr>
       <td>fallbackPlacement</td>