Add option to define a selection of MouseButtons to ignore

packages/vanilla/src/index.ts

@@ -1,7 +1,7 @@
 import {EventTarget} from './EventEmitter';
 import type {AreaLocation, Coordinates, ScrollEvent, SelectionEvents, SelectionOptions, SelectionStore} from './types';
 import {PartialSelectionOptions} from './types';
-import {css, frames, Frames, intersects, isSafariBrowser, isTouchDevice, off, on, selectAll, SelectAllSelectors, simplifyEvent} from './utils';
+import {css, frames, Frames, intersects, isSafariBrowser, isTouchDevice, off, on, selectAll, SelectAllSelectors, simplifyEvent, shouldTrigger} from './utils';
 
 // Re-export types
 export * from './types';
@@ -69,6 +69,7 @@ export default class SelectionArea extends EventTarget<SelectionEvents> {
             behaviour: {
                 overlap: 'invert',
                 intersect: 'touch',
+                triggers: [{button: 0, modifiers: ["ctrl", "alt", "meta"]}],
                 ...opt.behaviour,
                 startThreshold: opt.behaviour?.startThreshold ?
                     typeof opt.behaviour.startThreshold === 'number' ?
@@ -154,6 +155,9 @@ export default class SelectionArea extends EventTarget<SelectionEvents> {
         const {_options} = this;
         const {document} = this._options;
         const targetBoundingClientRect = target.getBoundingClientRect();
+
+        if (evt instanceof MouseEvent && !shouldTrigger(evt, _options.behaviour.triggers)) 
+            return;
 
         // Find start-areas and boundaries
         const startAreas = selectAll(_options.startAreas, _options.document);

packages/vanilla/src/types.ts

@@ -55,6 +55,25 @@ export interface Coordinates {
 export type TapMode = 'touch' | 'native';
 export type OverlapMode = 'keep' | 'drop' | 'invert';
 
+// https://developer.mozilla.org/en-US/docs/Web/API/MouseEvent/button#value
+export type MouseButton = 0  // Main
+                        | 1  // Auxiliary
+                        | 2  // Secondary
+                        | 3  // Fourth
+                        | 4; // Fifth
+
+export type Modifier = 'ctrl' 
+                     | 'meta' 
+                     | 'alt'
+                     | 'shift';
+
+export type Trigger = MouseButton | MouseButtonWithModifiers;
+
+export type MouseButtonWithModifiers =  {
+    button: MouseButton,
+    modifiers: Modifier[]
+};
+
 export interface Scrolling {
     speedDivider: number;
     manualSpeed: number;
@@ -77,6 +96,7 @@ export interface Behaviour {
     startThreshold: number | Coordinates;
     overlap: OverlapMode;
     scrolling: Scrolling;
+    triggers: Trigger[];
 }
 
 export interface SelectionOptions {

packages/vanilla/src/utils/index.ts

@@ -4,3 +4,4 @@ export * from './intersects';
 export * from './selectAll';
 export * from './constants';
 export * from './frames';
+export * from './shouldTrigger';

packages/vanilla/src/utils/shouldTrigger.ts

@@ -0,0 +1,48 @@
+import { Modifier, Trigger } from "../types";
+
+type MouseEventModifierProperty = Extract<keyof MouseEvent, "altKey" | "ctrlKey" | "metaKey" | "shiftKey">;
+
+/**
+ * Determines whether a MouseEvent should execute until completion depending on 
+ * which button and modifier(s) are active for the MouseEvent. 
+ * The Event will execute to completion if ANY of the triggers "matches"
+ * @param event MouseEvent that should be checked
+ * @param triggers A list of Triggers that signify that the event should execute until completion
+ * @returns Whether the MouseEvent should execute until completion
+ */
+export function shouldTrigger(event: MouseEvent, triggers: Trigger[]): boolean {
+    for (const trigger of triggers) {
+        // The trigger requires only a specific button to be pressed
+        if (typeof trigger === "number") {
+            if (event.button === trigger) return true;
+        }
+
+        // The trigger requires a specific button to be pressed AND some modifiers
+        if (typeof trigger === "object") {
+            const reqButtonIsPressed = trigger.button === event.button;
+            const allReqModifiersArePressed = trigger.modifiers.reduce((doActivate, modifier) => {
+                const prop = modifierToMouseEventProperty(modifier);
+
+                if (prop === null) return false;
+
+                const modifierIsPressed = event[prop];
+
+                return doActivate && modifierIsPressed;
+            }, true);
+
+            if (reqButtonIsPressed && allReqModifiersArePressed) return true;
+        }
+    }
+
+    // By default we do not process the event
+    return false;
+}
+
+function modifierToMouseEventProperty(modifier: Modifier): MouseEventModifierProperty | null {
+    if (modifier === "alt") return "altKey";
+    if (modifier === "ctrl") return "ctrlKey";
+    if (modifier === "meta") return "metaKey";
+    if (modifier === "shift") return "shiftKey";
+
+    return null;
+}