Javascript drag and drop, resizing and gestures for modern desktop and mobile browsers.

Awesomeness includes:

• inertia
• snapping to a grid, custom anchors or paths.
• cross browser and device, supporting {Chrome,Firefox,Opera}' '{mobile,desktop}', ' and Internet Explorer 8+
• interaction with SVG elements
• being standalone (not yet another jQuery plugin)
• introducing 0 additional DOM elements
• having(a). fluent ().interface
• not modifying anything it doesn't own (except to support IE8 and to change the cursor (but you can disable that))

Demos

• http://interactjs.io has some demos showing drag and drop, gestures, ienrtia, snap and some other things.

• The html & svg demo shows div elements which can be dragged and dropped onto each other and resized by dragging the botom and right edges. The yellow elements are SVG elements (these won't show up on IE8).

• star.svg demonstrates interact.js being used within an SVG document.

• The snapping demo shows how flexible the grid and anchor snapping system is and it's pretty fun.

• This blog post on path snapping demonstrates and graphs some interesting path snapping functions.

interact.js began as a Google Summer of Code 2012 project for Biographer, a biological network layout and visualization tool. It uses interact.js to modify SVG elements and to pan and zoom the viewport using a mouse or touch screen device.

Example

var // x and y to keep the position that's been dragged to
    x = 0,
    y = 0,
    // vendor prefixes (prefices?)
    transformProp = 'transform' in document.body.style?
                'transform': 'webkitTransform' in document.body.style?
                    'webkitTransform': 'mozTransform' in document.body.style?
                        'mozTransform': 'oTransform' in document.body.style?
                            'oTransform': 'msTransform';

// make an Interactable of the document body element
interact(document.body)
    // make a draggable of the Interactable
    .draggable({
        // on(drag)move
        // could also have done interact(document.body).draggable(true).ondragmove = function...
        onmove: function (event) {
            x += event.dx;
            y += event.dy;

            // translate the document body by the change in pointer position
            document.body.style[transformProp] = 'translate(' + x + 'px, ' + y + 'px)';
        }
    })
    // you should really add listeners like this if you want to add multiple listeners
    .on('dragend', function (event) {
        console.log('dragged a distance of ' + 
            Math.sqrt(event.dx*event.dx + event.dy*event.dy) + 
            ' pixels to ' + event.pageX + ', ' + event.pageY);
    })
    // allow inertia throwing
    .inertia({
        resistance: 15;
    });
    // snap to the corners of the specified grid
    .snap({
        mdoe: 'grid',
        grid: {
            x: 100,
            y: 5
        },
        gridOffset: {
            x: 20,
            y: 10
        },
        range: Infinity // can also use -1 which gets changed to Infinity
    });
    

// you can also listen to InteractEvents for every Interactable
interact.on('dragstart', function (event) {
    console.log('starting drag from ' + event.x0 + ', ' + event.y0);
});

Documentation

http://interactjs.io/docs

Usage

Pass the element you want to interact with or a CSS selector string to interact. That returns an object with methods, notably draggable, resizable, gesturable, dropzone which let you allow or disallow the related actions and on which let's you add event listeners for InteractEvents and any DOM event. The InteractEvent types are {drag,resize,gesture}{start,move,end}', ' dragenter, dragleave and drop when dragging over dropzones.

Details

Interactables

The interact function adds mouse or touch event listeners to the object and returns an Interactable object which has several methods and properties to configure how it behaves and what it can do. These methods have a fluent interface so method calls can be chained nicely.

For example, to make a DOM element dragagble and resizable you can call the Interactable#set with an object with the properties you want to set

interact(document.getElementById('anElement'))
    .set({
        draggable: true,
        resizable: true
    });

or you can call each {action}able method with the options for each.

interact(document.getElementById('anElement'))
        .draggable (true)
        .resizable(true);

Acting

Now that the element has been made interactable, when it is clicked on or touched and then dragged, an action is determined depending on the input type and position of the event over the element. InteractEvents are then fired as the mouse/touch moves around the page until it is finally released or the window loses focus.

When a sequence of user actions results in an InteractEvent, that event type is fired and all listeners of that type which were bound to that Interactable or bound globally are called.

Even though InteractEvents are being fired, the element is not actually modified by interact.js at all. To do that, you need to add listeners for InteractEvents either to each Interactable or globally for all Interacables and style the element according to event data.

Listening

The InteractEvent types are {drag,resize,gesture}{start,move,end}, dragenter, dragleave and drop when dragging over dropzones.

To respond to an InteractEvent, you must add a listener for its event type either directly to an interactable Interactable#on(eventType, listenerFunction) or globally for all events of that type interact.on('resizemove', resizeElement). The InteractEvent object that was created is passed to these functions as the first parameter.

InteractEvent properties include the usual properties of mouse/touch events such as pageX/Y, clientX/Y, modifier keys etc. but also some properties providing information about the change in cordinates and event specific data. The table below displays all of these events.

InteractEvent properties

Common
x0, y0	Page x and y coordinates of the starting event
clientX0, clientY0	Client x and y coordinates of the starting event
dx, dy	Change in coordinates of the mouse/touch *
target	The element that is being interacted with

Drag
dragmove
dragEnter	The dropzone this Interactable was dragged over
dragLeave	The dropzone this Interactable was dragged out of
dragenter, dragLeave
draggable	The draggable that's over this dropzone

Drop
draggable	The dragagble that was dropped into this dropzone

Resize
axes	The axes the resizing is constrained to (x/y/xy)

Gesture
touches	The array of touches that triggered the event
distance	The distance between the event's first two touches
angle	The angle of the line made by the two touches
da	The change in angle since previous event
scale	The ratio of the distance of the start event to the distance of the current event
ds	The change in scale since the previous event
box	A box enclosing all touch points

* In interact move events, these are the changes since the previous InteractEvent. However, in end events, these are the changes from the position of the start event to the end event. In gesture events, coordinates are the averages of touch coordinates.

Interacting

To move an element in response to a dragmove, a listener can be bound that transforms the element accoding to dy and dx of the InteractEvent. It can also be done by having the element positioned absolute, fixed or relative and adding the change in coordinates to the top and left position of the element.

// Set element and listen for dragmove events
interact(element)
    .draggable({
        onmove: function(event) {
            var elementStyle = event.target.style;

            // Add the change in mouse/touch coordinates to the element's current position
            elementStyle.left =
                parseInt(elementStyle.left) + event.dx + "px";

            elementStyle.top =
                parseInt(elementStyle.top) + event.dy + "px";
        });

License

interact.js is released under the MIT License.