Merge pull request #3365 from plotly/slider-500

Warn if slider has more than 500 marks and use default instead

Author: T4rk1n

components/dash-core-components/src/fragments/Slider.react.js

@@ -17,6 +17,8 @@ import {
 } from '../utils/formatSliderTooltip';
 import LoadingElement from '../utils/LoadingElement';
 
+const MAX_MARKS = 500;
+
 const sliderProps = [
     'min',
     'max',
@@ -76,6 +78,21 @@ export default class Slider extends Component {
         } = this.props;
         const value = this.state.value;
 
+        // Check if marks exceed 500 limit for performance
+        let processedMarks = marks;
+        if (marks && typeof marks === 'object' && marks !== null) {
+            const marksCount = Object.keys(marks).length;
+            if (marksCount > MAX_MARKS) {
+                /* eslint-disable no-console */
+                console.error(
+                    `dcc.Slider: Too many marks (${marksCount}) provided. ` +
+                        `For performance reasons, marks are limited to 500. ` +
+                        `Using auto-generated marks instead.`
+                );
+                processedMarks = undefined;
+            }
+        }
+
         let tipProps, tipFormatter;
         if (tooltip) {
             /**
@@ -136,11 +153,16 @@ export default class Slider extends Component {
                     tipFormatter={tipFormatter}
                     style={{position: 'relative'}}
                     value={value}
-                    marks={sanitizeMarks({min, max, marks, step})}
-                    max={setUndefined(min, max, marks).max_mark}
-                    min={setUndefined(min, max, marks).min_mark}
+                    marks={sanitizeMarks({
+                        min,
+                        max,
+                        marks: processedMarks,
+                        step,
+                    })}
+                    max={setUndefined(min, max, processedMarks).max_mark}
+                    min={setUndefined(min, max, processedMarks).min_mark}
                     step={
-                        step === null && !isNil(marks)
+                        step === null && !isNil(processedMarks)
                             ? null
                             : calcStep(min, max, step)
                     }

components/dash-core-components/tests/integration/sliders/test_sliders.py

@@ -616,3 +616,50 @@ def test_sls016_sliders_format_tooltips(dash_dcc):
     dash_dcc.percy_snapshot("sliders-format-tooltips")
 
     assert dash_dcc.get_logs() == []
+
+
+def test_slsl017_marks_limit_500(dash_dcc):
+    """Test that slider works with exactly 500 marks"""
+    app = Dash(__name__)
+    marks_500 = {str(i): f"Mark {i}" for i in range(500)}
+    app.layout = html.Div(
+        [
+            dcc.Slider(id="slider", min=0, max=499, marks=marks_500, value=250),
+            html.Div(id="output"),
+        ]
+    )
+
+    @app.callback(Output("output", "children"), [Input("slider", "value")])
+    def update_output(value):
+        return f"Selected: {value}"
+
+    dash_dcc.start_server(app)
+    dash_dcc.wait_for_text_to_equal("#output", "Selected: 250")
+
+    # No warnings should be logged for 500 marks
+    assert dash_dcc.get_logs() == []
+
+
+def test_slsl018_marks_limit_exceeded(dash_dcc):
+    """Test behavior when marks exceed 500 limit"""
+    app = Dash(__name__)
+    marks_501 = {str(i): f"Mark {i}" for i in range(501)}
+    app.layout = html.Div(
+        [
+            dcc.Slider(id="slider", min=0, max=500, marks=marks_501, value=250),
+            html.Div(id="output"),
+        ]
+    )
+
+    @app.callback(Output("output", "children"), [Input("slider", "value")])
+    def update_output(value):
+        return f"Selected: {value}"
+
+    dash_dcc.start_server(app)
+    dash_dcc.wait_for_text_to_equal("#output", "Selected: 250")
+
+    # Check that warning is logged
+    logs = dash_dcc.get_logs()
+    assert len(logs) > 0
+    warning_found = any("Too many marks" in log["message"] for log in logs)
+    assert warning_found, "Expected warning about too many marks not found in logs"