ToolTip in Angular Sankey component

18 Nov 201818 minutes to read

The Sankey Chart provides tooltips that surface contextual details for hovered elements without cluttering the diagram. Tooltips display additional information when users hover over nodes or links in the Sankey Chart. You can enable and customize tooltips using the tooltip property and by injecting the SankeyTooltip module.

This guide outlines how to enable and customize tooltips in the React Sankey Chart.

Tooltip Settings Properties

The following table lists the main tooltip configuration properties:

Property Type Default Description
enable boolean true Enables or disables the tooltip display.
fill string null Background fill color of the tooltip.
opacity number 0.75 Opacity of the tooltip container (0 to 1).
textStyle object null Text styling for the tooltip content.
nodeFormat string ‘$name : $value’ Format string for node tooltips.
linkFormat string ‘$start.name $start.value → $target.name $target.value’ Format string for link tooltips.
enableAnimation boolean true Toggles tooltip animation.
duration number 300 Animation duration in milliseconds.
fadeOutDuration number 1000 Fade-out duration in milliseconds.
fadeOutMode string ‘Move’ Fade-out animation mode (‘Move’, ‘Fade’, ‘Delay’).

Basic Tooltip Configuration

Enable tooltips with default formatting.

import { Component } from '@angular/core';
import { SankeyAllModule } from '@syncfusion/ej2-angular-charts';
import {
  SankeyTooltipService,
  SankeyLegendService,
  SankeyExportService
} from '@syncfusion/ej2-angular-charts';

@Component({
  imports: [SankeyAllModule],
  providers: [
    SankeyTooltipService,
    SankeyLegendService,
    SankeyExportService
  ],
  standalone: true,
  selector: 'app-container',
  template: `
    <div class="control-pane">
      <div class="control-section"  id="sankey-container">
  <ejs-sankey
    width="90%"
    height="450px"
    [tooltip]=tooltip>

    <e-sankey-nodes>
      <e-sankey-node id="Agricultural Waste"></e-sankey-node>
      <e-sankey-node id="Biomass Residues"></e-sankey-node>
      <e-sankey-node id="Bio-conversion"></e-sankey-node>
      <e-sankey-node id="Liquid Biofuel"></e-sankey-node>
      <e-sankey-node id="Electricity"></e-sankey-node>
      <e-sankey-node id="Heat"></e-sankey-node>
    </e-sankey-nodes>

    <e-sankey-links>
      <e-sankey-link sourceId="Agricultural Waste" targetId="Bio-conversion" [value]="84.152"></e-sankey-link>
      <e-sankey-link sourceId="Biomass Residues" targetId="Bio-conversion" [value]="24.152"></e-sankey-link>
      <e-sankey-link sourceId="Bio-conversion" targetId="Liquid Biofuel" [value]="10.597"></e-sankey-link>
      <e-sankey-link sourceId="Bio-conversion" targetId="Electricity" [value]="36.862"></e-sankey-link>
      <e-sankey-link sourceId="Bio-conversion" targetId="Heat" [value]="60.845"></e-sankey-link>
    </e-sankey-links>

  </ejs-sankey>
      </div>
    </div>`
})
export class AppComponent {
  public tooltip={ enable: true };
 }
import { bootstrapApplication } from '@angular/platform-browser';
import { AppComponent } from './app.component';
import 'zone.js';
bootstrapApplication(AppComponent).catch((err) => console.error(err));

Customizing Tooltip Appearance

Adjust tooltip appearance and behavior using tooltip configuration properties:

  • Enable: Shows or hides tooltips.
  • Fill: Sets background color.
  • Opacity: Controls transparency (0 to 1). The default value is 0.75.
  • TextStyle: Configures font size, family, weight, and color for the tooltip text.
  • EnableAnimation: Toggles animation. Default: true.
  • Duration: Animation duration in milliseconds. The default value is 300.
  • FadeOutDuration: Fade-out duration in milliseconds. The default value is 1000.

Example customization:

import { Component } from '@angular/core';
import { SankeyAllModule } from '@syncfusion/ej2-angular-charts';
import {
  SankeyTooltipService,
  SankeyLegendService,
  SankeyExportService
} from '@syncfusion/ej2-angular-charts';

@Component({
  imports: [SankeyAllModule],
  providers: [
    SankeyTooltipService,
    SankeyLegendService,
    SankeyExportService
  ],
  standalone: true,
  selector: 'app-container',
  template: `
    <div class="control-pane">
      <div class="control-section"  id="sankey-container">
      <ejs-sankey
    width="90%"
    height="450px"
    [tooltip]="tooltipConfig">

    <e-sankey-nodes>
      <e-sankey-node id="Agricultural Waste"></e-sankey-node>
      <e-sankey-node id="Biomass Residues"></e-sankey-node>
      <e-sankey-node id="Bio-conversion"></e-sankey-node>
      <e-sankey-node id="Liquid Biofuel"></e-sankey-node>
      <e-sankey-node id="Electricity"></e-sankey-node>
      <e-sankey-node id="Heat"></e-sankey-node>
    </e-sankey-nodes>

    <e-sankey-links>
      <e-sankey-link sourceId="Agricultural Waste" targetId="Bio-conversion" [value]="84.152"></e-sankey-link>
      <e-sankey-link sourceId="Biomass Residues" targetId="Bio-conversion" [value]="24.152"></e-sankey-link>
      <e-sankey-link sourceId="Bio-conversion" targetId="Liquid Biofuel" [value]="10.597"></e-sankey-link>
      <e-sankey-link sourceId="Bio-conversion" targetId="Electricity" [value]="36.862"></e-sankey-link>
      <e-sankey-link sourceId="Bio-conversion" targetId="Heat" [value]="60.845"></e-sankey-link>
    </e-sankey-links>

  </ejs-sankey>
      </div>
    </div>`
})
export class AppComponent {
  public tooltipConfig = {
    enable: true,
    textStyle: {
      fontFamily: 'Arial',
      fontStyle: 'normal',
      fontWeight: '500',
      size: '14px',
      color: '#000'
    },
    fill: '#F3F3F3',
    border: {
      color: '#666',
      width: 1
    }
  };
}
import { bootstrapApplication } from '@angular/platform-browser';
import { AppComponent } from './app.component';
import 'zone.js';
bootstrapApplication(AppComponent).catch((err) => console.error(err));

Format Strings

Format strings provide a simple way to customize tooltip content without custom templates.

Node Tooltip Format

Format string placeholders for node tooltips:

  • $name – Node label
  • $value – Node value (sum of incoming links)

Format string placeholders for link tooltips:

  • $start.name – Source node label
  • $start.value – Source node value
  • $target.name – Target node label
  • $target.value – Target node value
  • $value – Link value

Example with custom format strings:

import { Component } from '@angular/core';
import { SankeyAllModule } from '@syncfusion/ej2-angular-charts';
import {
  SankeyTooltipService,
  SankeyLegendService,
  SankeyExportService
} from '@syncfusion/ej2-angular-charts';

@Component({
  imports: [SankeyAllModule],
  providers: [
    SankeyTooltipService,
    SankeyLegendService,
    SankeyExportService
  ],
  standalone: true,
  selector: 'app-container',
  template: `
  <div class="control-pane">
      <div class="control-section"  id="sankey-container">
  <ejs-sankey
    width="90%"
    height="450px"
    [tooltip]="tooltipConfig">

    <e-sankey-nodes>
      <e-sankey-node id="Agricultural Waste"></e-sankey-node>
      <e-sankey-node id="Biomass Residues"></e-sankey-node>
      <e-sankey-node id="Bio-conversion"></e-sankey-node>
      <e-sankey-node id="Liquid Biofuel"></e-sankey-node>
      <e-sankey-node id="Electricity"></e-sankey-node>
      <e-sankey-node id="Heat"></e-sankey-node>
    </e-sankey-nodes>

    <e-sankey-links>
      <e-sankey-link sourceId="Agricultural Waste" targetId="Bio-conversion" [value]="84.152"></e-sankey-link>
      <e-sankey-link sourceId="Biomass Residues" targetId="Bio-conversion" [value]="24.152"></e-sankey-link>
      <e-sankey-link sourceId="Bio-conversion" targetId="Liquid Biofuel" [value]="10.597"></e-sankey-link>
      <e-sankey-link sourceId="Bio-conversion" targetId="Electricity" [value]="36.862"></e-sankey-link>
      <e-sankey-link sourceId="Bio-conversion" targetId="Heat" [value]="60.845"></e-sankey-link>
    </e-sankey-links>

  </ejs-sankey>
      </div>
    </div>`
})
export class AppComponent {
  public tooltipConfig = {
    enable: true,
    nodeTemplate: '${name}: ${value} TBtu',
    linkTemplate: '${start.name}: ${start.out} TBtu → ${target.name}: ${target.in} TBtu'
  };
}
import { bootstrapApplication } from '@angular/platform-browser';
import { AppComponent } from './app.component';
import 'zone.js';
bootstrapApplication(AppComponent).catch((err) => console.error(err));

Inline tooltip formatting

The tooltip content can be formatted directly within the nodeFormat and linkFormat properties by adding DateTime or number format specifiers to supported tooltip tokens. This allows you to control how node and link values are displayed without using additional events.

A format specifier is applied by adding a colon (:) followed by the required format. Sankey tooltip supports both $ placeholders and ${} placeholders for displaying tooltip values. When a value needs to be formatted, use the ${} placeholder syntax with a colon (:) followed by the required format specifier.

For example:

public tooltip = {
    enable: true,
    nodeFormat: '$name : ${value:n2}',
    linkFormat: '$start.name (${start.out:n2}) → ${target.name} (${target.in:n2}) : ${value:n2}'
};

In the above example, $name and $start.name display text values directly, while ${value:n2}, ${start.out:n2}, and ${target.in:n2} display numeric values with two decimal places.

Sankey tooltip values can be displayed in either of the following ways:

  • $start.name or ${start.name} – Displays the source node name.
  • $target.name or ${target.name} – Displays the target node name.
  • $value or ${value} – Displays the node or link value.

To apply formatting, use the ${} syntax with the required format specifier. For example, ${value:n2} displays the value with two decimal places.

Inline formatting can be applied to the following tooltip placeholders:

  • $name or ${name} – Specifies the name or label of the hovered node.
  • $value, ${value}, or ${value:n2} – Specifies the value of the hovered node or link.
  • $start.name or ${start.name} – Specifies the name of the source node in a link tooltip.
  • $start.value, ${start.value}, or ${start.value:n2} – Specifies the value of the source node in a link tooltip.
  • $start.out, ${start.out}, or ${start.out:n2} – Specifies the outgoing value from the source node in a link tooltip.
  • $target.name or ${target.name} – Specifies the name of the target node in a link tooltip.
  • $target.value, ${target.value}, or ${target.value:n2} – Specifies the value of the target node in a link tooltip.
  • $target.in, ${target.in}, or ${target.in:n2} – Specifies the incoming value to the target node in a link tooltip.

Important: Sankey tooltip placeholders can be used in both $placeholder and ${placeholder} formats, such as $start.name or ${start.name}. However, when applying number formatting, the ${placeholder:format} syntax must be used, such as ${value:n2}, ${start.out:n2}, and ${target.in:n2}. Formatting is applied only when the resolved value supports the specified format. String tokens, such as ${name}, ${start.name}, and ${target.name}, are displayed as plain text and do not support number formatting.

The following number formats are supported:

  • n2 – number with two decimal places
  • n0 – number without decimals
  • c2 – currency format
  • p1 – percentage format
  • e1 – exponential notation

If the specified format does not match the resolved value type, the original value is displayed.

import { Component } from '@angular/core';
import { SankeyAllModule } from '@syncfusion/ej2-angular-charts';
import { SankeyTooltipService, SankeyLegendService } from '@syncfusion/ej2-angular-charts';

@Component({
  imports: [SankeyAllModule],
  providers: [ SankeyTooltipService, SankeyLegendService],
  standalone: true,
  selector: 'app-container',
  template: `<ejs-sankey id="sankey-container" width="90%" height="450px" [tooltip]="tooltip" [legendSettings]="legendSettings">
              <e-sankey-nodes>
                <e-sankey-node id="Agricultural Waste"></e-sankey-node>
                <e-sankey-node id="Biomass Residues"></e-sankey-node>
                <e-sankey-node id="Bio-conversion"></e-sankey-node>
                <e-sankey-node id="Liquid Biofuel"></e-sankey-node>
                <e-sankey-node id="Electricity"></e-sankey-node>
                <e-sankey-node id="Heat"></e-sankey-node>
              </e-sankey-nodes>
              <e-sankey-links>
                <e-sankey-link sourceId="Agricultural Waste" targetId="Bio-conversion" [value]="84.152"></e-sankey-link>
                <e-sankey-link sourceId="Biomass Residues" targetId="Bio-conversion" [value]="24.152"></e-sankey-link>
                <e-sankey-link sourceId="Bio-conversion" targetId="Liquid Biofuel" [value]="10.597"></e-sankey-link>
                <e-sankey-link sourceId="Bio-conversion" targetId="Electricity" [value]="36.862"></e-sankey-link>
                <e-sankey-link sourceId="Bio-conversion" targetId="Heat" [value]="60.845"></e-sankey-link>
              </e-sankey-links>
</ejs-sankey>`
})
export class AppComponent {
 
public tooltip: Object = {
    enable: true,
    nodeFormat: '${name} : ${value:n2} TBtu',
    linkFormat: '${start.name} : ${start.out:n2} TBtu → ${target.name} : ${target.in:n2} TBtu<br>Flow: ${value:n2} TBtu'
  };

  public legendSettings: Object = {
    visible: true
  };
}
import { bootstrapApplication } from '@angular/platform-browser';
import { AppComponent } from './app.component';
import 'zone.js';
bootstrapApplication(AppComponent).catch((err) => console.error(err));

Advanced Tooltip Configuration

Tooltip Rendering Event

Use tooltipRendering to programmatically modify tooltip content before display.

import { Component } from '@angular/core';
import { SankeyAllModule, SankeyTooltipRenderEventArgs } from '@syncfusion/ej2-angular-charts';
import {
  SankeyTooltipService,
  SankeyLegendService,
  SankeyExportService
} from '@syncfusion/ej2-angular-charts';

@Component({
  imports: [SankeyAllModule],
  providers: [
    SankeyTooltipService,
    SankeyLegendService,
    SankeyExportService
  ],
  standalone: true,
  selector: 'app-container',
  template: `
  <div class="control-pane">
      <div class="control-section"  id="sankey-container">
      <ejs-sankey
    width="90%"
    height="450px"
    [tooltip]="{ enable: true }"
    (tooltipRendering)="onTooltipRender($event)">

    <e-sankey-nodes>
      <e-sankey-node id="Agricultural Waste"></e-sankey-node>
      <e-sankey-node id="Biomass Residues"></e-sankey-node>
      <e-sankey-node id="Bio-conversion"></e-sankey-node>
      <e-sankey-node id="Liquid Biofuel"></e-sankey-node>
      <e-sankey-node id="Electricity"></e-sankey-node>
      <e-sankey-node id="Heat"></e-sankey-node>
    </e-sankey-nodes>

    <e-sankey-links>
      <e-sankey-link sourceId="Agricultural Waste" targetId="Bio-conversion" [value]="84.152"></e-sankey-link>
      <e-sankey-link sourceId="Biomass Residues" targetId="Bio-conversion" [value]="24.152"></e-sankey-link>
      <e-sankey-link sourceId="Bio-conversion" targetId="Liquid Biofuel" [value]="10.597"></e-sankey-link>
      <e-sankey-link sourceId="Bio-conversion" targetId="Electricity" [value]="36.862"></e-sankey-link>
      <e-sankey-link sourceId="Bio-conversion" targetId="Heat" [value]="60.845"></e-sankey-link>
    </e-sankey-links>

  </ejs-sankey>
      </div>
    </div>`
})
export class AppComponent {

 onTooltipRender(args: SankeyTooltipRenderEventArgs): void {
    if (args.link) {
      args.text = `Flow: ${args.link.sourceId} → ${args.link.targetId} (${args.link.value})`;
    } else if (args.node) {
      args.text = `Node: ${args.node.id}`;
    }
  }
}
import { bootstrapApplication } from '@angular/platform-browser';
import { AppComponent } from './app.component';
import 'zone.js';
bootstrapApplication(AppComponent).catch((err) => console.error(err));

Disabling Tooltips

To disable tooltips:

const tooltip = { enable: false };

Key Considerations

  • Keep Text Concise: Keep tooltip text concise and readable.
  • Ensure Contrast: Ensure sufficient contrast for tooltip text and background.
  • Use Format Strings: Prefer nodeFormat and linkFormat for simple content customization without requiring custom rendering logic.
  • Animation Tuning: Tune animation durations to balance responsiveness and polish.
  • Performance: Use format strings instead of complex rendering logic for better performance.
  • Relevant Information: Show only relevant and helpful information.
  • Consistent Styling: Maintain consistent tooltip styling across your application.