Add Dart Map .addAll() term entry

content/dart/concepts/map/terms/add-all/add-all.md

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+---
+Title: '.addAll()'
+Description: 'Adds all key-value pairs from another `Map` into the current map.'
+Subjects:
+  - 'Computer Science'
+  - 'Data Science'
+Tags:
+  - 'Dart'
+  - 'Map'
+  - 'Methods'
+CatalogContent:
+  - 'learn-dart'
+  - 'paths/computer-science'
+---
+
+In Dart, the **`.addAll()`** method adds all key-value pairs from another `Map` into an existing `Map`. This is commonly used when merging maps or inserting multiple entries at once.
+
+If a key from the source map already exists in the target map, its value will be replaced by the value from the source map.
+
+## Syntax
+
+```pseudo
+mapVariable.addAll(otherMap)
+```
+
+`mapVariable` is the `Map` object to which new key–value pairs will be added.
+
+**Parameters:**
+
+- `otherMap`: A map whose key–value pairs are added to `mapVariable`. If a key already exists, its value is overwritten.
+
+**Return value:**
+
+This method returns `void`. The original map is modified in place.
+
+## Example
+
+The following example demonstrates how `.addAll()` can be used to merge two maps:
+
+```dart
+void main() {
+  Map<String, int> inventory = {
+    'Apples': 5,
+    'Bananas': 3
+  };
+
+  Map<String, int> newItems = {
+    'Oranges': 4,
+    'Grapes': 10
+  };
+
+  inventory.addAll(newItems);
+
+  print(inventory);
+}
+```
+
+The output of this code is as follows:
+
+```shell
+{Apples: 5, Bananas: 3, Oranges: 4, Grapes: 10}
+```