dcc.Location props fix for callbacks (plotly#774)

* Added conditionally set props

* Updated changelog.

* Added integration test to check callbacks

Author: HammadTheOne

packages/dash-core-components/CHANGELOG.md

@@ -8,6 +8,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - [#768](https://github.com/plotly/dash-core-components/pull/768) Added title property to dcc.Link
 - [#776](https://github.com/plotly/dash-core-components/pull/776) Update dcc.Link to set href as children if children not defined. Makes href a required prop as well.
 - [#767](https://github.com/plotly/dash-core-components/pull/767) Updated dcc.Link to respond to click modifiers, and added a target prop.
+- [#774](https://github.com/plotly/dash-core-components/pull/774) Fixed dcc.Location firing callbacks for wrong property. 
 
 ## [1.8.1] -2020-02-27
 ### Added

packages/dash-core-components/src/components/Location.react.js

@@ -86,12 +86,22 @@ export default class Location extends Component {
 
     onLocationChange() {
         const {setProps} = this.props;
-        setProps({
-            pathname: window.location.pathname,
-            href: window.location.href,
-            hash: window.location.hash,
-            search: window.location.search,
-        });
+        const propsToChange = {};
+
+        if (this.props.pathname !== window.location.pathname) {
+            propsToChange.pathname = window.location.pathname;
+        }
+        if (this.props.href !== window.location.href) {
+            propsToChange.href = window.location.href;
+        }
+        if (this.props.hash !== window.location.hash) {
+            propsToChange.hash = window.location.hash;
+        }
+        if (this.props.search !== window.location.search) {
+            propsToChange.search = window.location.search;
+        }
+
+        setProps(propsToChange);
 
         History.dispatchChangeEvent();
     }

packages/dash-core-components/tests/integration/location/test_location_callback.py

@@ -0,0 +1,26 @@
+import pytest
+import dash
+from dash.dependencies import Input, Output
+import dash_core_components as dcc
+import dash_html_components as html
+
+
+@pytest.mark.DCC774
+def test_loca001_callbacks(dash_dcc):
+    app = dash.Dash(__name__)
+    app.layout = html.Div([
+        dcc.Location(
+            id='location',
+            refresh=False
+        ),
+        html.A('Anchor Link 1', href='#div'),
+        html.Div(id='div')
+    ])
+
+    @app.callback(Output('div', 'children'), [Input('location', 'pathname')])
+    def update_path(path):
+        return path
+
+    dash_dcc.start_server(app)
+
+    dash_dcc.wait_for_text_to_equal('#div', '/')