DFlex Drag and Drop API

npm install @dflex/dnd

DFlex DnD depends on three principles to achieve DOM interactivity:

Register element in the store.
Start dragging when mouse is down.
End dragging to release element when mouse is up.

import { store, DnD } from "@dflex/dnd";

Each element should be registered in DFlex DnD Store in order to be active for drag and drop later.

store.register(RegisterInputOpts): void;

Where RegisterInputOpts is an object with the following properties:

id: string Targeted element-id.
depth?: number The depth of targeted element starting from zero (The default value is zero).
readonly?: boolean True for elements that won't be transformed during DnD but belongs to the same interactive container.

The responsive drag and drop session should be created when onmousedown is fired. So it can initialize the element and its siblings before start dragging.

const dflexDnD = new DnD(id, coordinate, opts);

id: string registered element-id in the store.
coordinate: AxesPoint is an object with {x: number, y: number} contains the coordinates of the mouse/touch click.
opts?: DFlexDnDOpts is DnD options object. You can see DFlex DnD options full documentation by clicking here.

dflexDnD.dragAt(x, y);

x: number is event.clientX, the horizontal click coordinate.
y: number is event.clientY, the vertical click coordinate.

dflexDnD.endDragging();

It's necessary to cleanup the element from store when the element won't be used or will be removed/unmounted from the DOM to prevent any potential memory leaks.

store.unregister(id: string): void

You can pass options when creating a DnD instance that controls each element individually. So your options can be different from each other.

The threshold object defines when the dragging event should be fired and triggers the response of other sibling elements.

interface ThresholdPercentages {
  /** vertical threshold in percentage from 0-100 */
  vertical: number;

  /** horizontal threshold in percentage from 0-100 */
  horizontal: number;
}

interface DFlexDnDOpts {
  // ... other options.
  threshold?: Partial<ThresholdPercentages>;
}

{
  "threshold": {
    "vertical": 60,
    "horizontal": 60
  }
}

DFlex is built to manipulate DOM elements with transformation indefinitely. This means you can always drag and drop elements without reconstruction of the DOM. Still, it comes with a reconciler that tracks elements' changes and only reconciles the elements that have changed their position from their origin.

interface CommitInterface {
  enableAfterEndingDrag: boolean;
  enableForScrollOnly: boolean;
}

interface DFlexDnDOpts {
  // ... other options.
  commit?: Partial<CommitInterface>;
}

{
  "commit": {
    "enableAfterEndingDrag": true,
    "enableForScrollOnly": true
  }
}

You can define the dragging restrictions for each element relative:

Element position.
Element parent container.
Screen viewport (automatically enabled).

interface Restrictions {
  self: {
    allowLeavingFromTop: boolean;
    allowLeavingFromBottom: boolean;
    allowLeavingFromLeft: boolean;
    allowLeavingFromRight: boolean;
  };
  container: {
    allowLeavingFromTop: boolean;
    allowLeavingFromBottom: boolean;
    allowLeavingFromLeft: boolean;
    allowLeavingFromRight: boolean;
  };
}

interface DFlexDnDOpts {
  // ... other options.
  restrictions?: {
    self?: Partial<Restrictions["self"]>;
    container?: Partial<Restrictions["container"]>;
  };
}

{
  "restrictions": {
    "self": {
      "allowLeavingFromTop": true,
      "allowLeavingFromBottom": true,
      "allowLeavingFromLeft": true,
      "allowLeavingFromRight": true
    },
    "container": {
      "allowLeavingFromTop": true,
      "allowLeavingFromBottom": true,
      "allowLeavingFromLeft": true,
      "allowLeavingFromRight": true
    }
  }
}

interface ScrollOptions {
  enable?: boolean;
  initialSpeed?: number;
  threshold?: Partial<ThresholdPercentages>;
}

interface DFlexDnDOpts {
  // ... other options.
  scroll?: Partial<ScrollOptions>;
}

{
  "scroll": {
    "enable": true,
    "initialSpeed": 10,
    "threshold": {
      "vertical": 15,
      "horizontal": 15
    }
  }
}

DFlex has three (3) types of custom events.

// DFlex event handler.
const onDFlexEvent = (e: DFlexEvents) => {
  // Do something.
  console.log(`onDFlexEvent: ${e.type}`, e.detail);
};

// Dragged Events.
const ON_OUT_CONTAINER = "$onDragOutContainer";
const ON_OUT_THRESHOLD = "$onDragOutThreshold";

//  Interactivity Events.
const ON_DRAG_OVER = "$onDragOver";
const ON_DRAG_LEAVE = "$onDragLeave";

// Sibling Events.
const ON_LIFT_UP = "$onLiftUpSiblings";
const ON_MOVE_DOWN = "$onMoveDownSiblings";

// Capture DFlex event.
document.addEventListener(
  ON_OUT_CONTAINER /** or another event */,
  onDFlexEvent
);

// Remove it later when dragging is done.
document.removeEventListener(
  ON_OUT_CONTAINER /** or another event */,
  onDFlexEvent
);

It's an event related to capturing dragged positions. This event is fired when the dragged is out of its threshold position $onDragOutContainer or out of its container $onDragOutThreshold.

interface PayloadDraggedEvent {
  /** Returns element id in the registry  */
  id: string;

  /** Returns dragged temp index */
  index: number;
}

/** For dragged out of threshold or container event. */
type DFlexDraggedEvent = CustomEvent<PayloadDraggedEvent>;

It's an event related to capturing dragged interactions with other elements. This event is fired when the dragged is over another element $onDragOver or when the dragged is leaving the occupied position $onDragLeave.

interface PayloadInteractivityEvent {
  /** Returns element id in the registry  */
  id: string;

  /** Returns element current index */
  index: number;

  /** Returns the element that triggered the event  */
  target: HTMLElement;
}

/** For dragged over an element or leaving an element. */
type DFlexInteractivityEvent = CustomEvent<PayloadInteractivityEvent>;

It's an event related to capturing siblings' positions. This event is fired when the siblings are lifting up $onLiftUpSiblings or moving down $onMoveDownSiblings

interface PayloadSiblingsEvent {
  /** Returns the index where the dragged left  */
  from: number;

  /** Returns the last index effected of the dragged leaving/entering  */
  to: number;

  /** Returns an array of sibling ids in order  */
  siblings: string[];
}

/** When dragged movement triggers the siblings up/down. */
type DFlexSiblingsEvent = CustomEvent<PayloadSiblingsEvent>;

DFlex listeners are more generic than the custom events and responsible for monitoring the entire layout and reporting back to you.

DFlex has two (2) types of listeners:

// app/index.js

const unsubscribeLayout = store.listeners.subscribe((e) => {
  console.info("new layout state", e);
}, "layoutState");

// call it later for clear listeners from memory.
unsubscribeLayout();

const unsubscribeMutation = store.listeners.subscribe((e) => {
  console.info("new mutation state", e);
}, "mutation");

// call it later for clear listeners from memory.
unsubscribeMutation();

Responsible for monitoring any change that happens to layout interactivity.

type LayoutState =
  | "pending" // when DnD is initiated but not activated yet.
  | "ready" // When clicking over the registered element. The element is ready but not being dragged.
  | "dragging" // as expected.
  | "dragEnd" // as expected.
  | "dragCancel"; // When releasing the drag without settling in the new position.

interface DFlexLayoutStateEvent {
  type: "layoutState";
  status: LayoutState;
}

Responsible for monitoring DOM mutation that happens during reconciliation.

type ElmMutationType = "committed";

interface DFlexElmMutationEvent {
  type: "mutation";
  status: ElmMutationType;
  payload: {
    target: HTMLElement; // HTML element container.
    ids: string[]; // Committed Elements' id in order.
  };
}

DFlex elements are serialized and exported accordingly.

store.getSerializedElm(elmID: string): DFlexSerializedElement | null

type DFlexSerializedElement = {
  type: string;
  version: number;
  id: string;
  translate: PointNum | null;
  grid: PointNum;
  order: DFlexDOMGenOrder;
  initialPosition: AxesPoint;
  rect: BoxRectAbstract;
  hasTransformedFromOrigin: boolean;
  hasPendingTransformation: boolean;
  isVisible: boolean;
};

DFlex scroll containers are serialized and exported accordingly. You can get any scroll container for any registered element id.

store.getSerializedScrollContainer(elmID: string): DFlexSerializedScroll | null

type DFlexSerializedScroll = {
  type: string;
  version: number;
  key: string;
  hasOverFlow: AxesPoint<boolean>;
  hasDocumentAsContainer: boolean;
  scrollRect: AbstractBox;
  scrollContainerRect: AbstractBox;
  invisibleDistance: AbstractBox;
  visibleScreen: Dimensions;
};

Commit changes to the DOM. commit will always do surgical reconciliation. and it's the same function that's used in the options

store.commit(): void

True when DFlex is not transforming any elements and not executing any task.

isLayoutAvailable(): boolean

safely removing element from store.

store.unregister(id: string): void

To destroy all DFlex instances. This is what you should do when you are done with DnD completely and your app is about to be closed.

store.destroy(): void;