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# Simulating DOM Events

When creating automated tests for your application or modules, you need to be able to mock user events. The DOM supports creating native events that behave essentially the same as user generated events, though without the associated browser default behaviors (e.g. following a link on click).

The `event-simulate` module adds the `Y.Event.simulate` method for working with raw DOM nodes, but for most cases, the `node-event-simulate` module is the right choice, since it allows you to call the `simulate` method directly from the `Node`.

## Simulating Mouse Events

There are seven mouse events that can be simulated:

- `click`
- `dblclick`
- `mousedown`
- `mouseup`
- `mouseover`
- `mouseout`
- `mousemove`

Each event is fired by calling `simulate()` and passing in two arguments: the type of event to fire and an optional object specifying additional information for the event. To simulate a click on the document's body element, for example, the following code can be used:

    YUI().use('node-event-simulate', function(Y) {

        Y.one("body").simulate("click");
    });

This code simulates a click with all of the default properties on the `event` object. To specify additional information, such as the Shift key being down, the second argument must be used and the exact DOM name for the event property specified (there is browser-normalizing logic that translates these into browser-specific properties when necessary):

    Y.one("body").simulate("click", { shiftKey: true });

In this updated example, a click event is fired on the document's body while simulating that the Shift key is down.

The extra properties to specify vary depending on the event being simulated and are limited to this list:

`detail`
  Indicates the number of times a button was clicked (DOM-compliant browsers only).
`screenX`, `screenY`
  Coordinates of the mouse event in relation to the entire screen (DOM-compliant browsers only).
`clientX`, `clientY`
  Coordinates of the mouse event in relation to the browser client area.
`ctrlKey`, `altKey`, `shiftKey`, `metaKey`
  The state of the Ctrl, Alt, Shift, and Meta keys, respectively (true for down, false for up).
`button`
  The button being used for the event, 0 for left (default), 1 for right, 2 for center.
`relatedTarget`
  the element the mouse moved from (during a `mouseover` event) or to (during a `mouseout` event).

    YUI().use('node-event-simulate', function(Y) {

        var node = Y.one("#myDiv");

        //simulate a click Alt key down
        node.simulate("click", { altKey: true});

        //simulate a double click with Ctrl key down
        node.simulate("dblclick", { ctrlKey: true });

        //simulate a mouse over
        node.simulate("mouseover", { relatedTarget: document.body });

        //simulate a mouse out
        node.simulate("mouseout", { relatedTarget: document.body });

        //simulate a mouse down at point (100,100) in the client area
        node.simulate("mousedown", { clientX: 100, clientY: 100 });

        //simulate a mouse up at point (100,100) in the client area
        node.simulate("mouseup", { clientX: 100, clientY: 100 });

        //simulate a mouse move at point (200, 200) in the client area
        node.simulate("mousemove", { clientX: 200, clientY: 200 });
    });

## Simulating Key Events

There are three key event simulations available:

- `keyup`
- `keydown`
- `keypress`

As with the mouse events, key events are simulated using `simulate()`. For `keyup` and `keydown`, the `keyCode` property must be specified; for `keypress`, the `charCode` property must be included. In many cases, `keyCode` and `charCode` may be the same value to represent the same key (97, for instance, represents the "A" key as well as being the ASCII code for the letter "a"). For example:

    YUI().use('node-event-simulate', function(Y) {

        var node = Y.one("#myDiv");

        //simulate a keydown on the A key
        node.simulate("keydown", { keyCode: 97 });

        //simulate a keyup on the A key
        node.simulate("keyup", { keyCode: 97 });

        //simulate typing "a"
        node.simulate("keypress", { charCode: 97 });
    });

Key events also support the `ctrlKey`, `altKey`, `shiftKey`, and `metaKey` event properties.

Note: Due to differences in browser implementations, key events may not be simulated in the same manner across all browsers. For instance, when simulating a keypress event on a textbox, only Firefox will update the textbox with the new character of the key that was simulated to be pressed. For other browsers, the events are still registered and all event handlers are called, however, the textbox display and `value` property are not updated. These differences should go away as browser support for simulated events improves in the future.

## Simulating UI Events

There are several UI event simulations available:

- `blur`
- `change`
- `focus`
- `resize`
- `scroll`
- `select`

As with the other events, UI events are simulated using `simulate()`. There are no properties that are required to simulate UI events as these events don't carry extra information. Some examples:

    YUI().use('node-event-simulate', function(Y) {

        var node = Y.one("#myInput");

        //simulate a change event
        node.simulate("change");

        //simulate a select event
        node.simulate("select");
    });

## Simulating Touch Gestures

There are several high level gesture simulations primarily targeted for smartphones, tablets, and other touch-enabled devices. Single touch gestures such as `tap` and `flick` are simulated using Mouse Events on desktop or mobile devices where creating Touch Events are not supported. All gesture simulations are done by calling the `simulateGesture()` method against a Node instance. The method is asynchronous by default so an optional callback function can be passed.

`tap`
  Single finger gesture to simulate a tap. Default is to simulate one tap but it can be configured to simulate any number of taps.
`doubletap`
  Single finger gesture to simulate double taps.
`press`
  Single finger gesture to simulate a long press.
`move`
  Single finger gesture to simulate a move. It simulates moving one finger straight in any direction.
`flick`
  Single finger gesture to simulate the flick gesture. It simulates moving one finger with a certain velocity along either an X or Y axis.
`pinch`
  Two finger gesture to simulate pinch and spread gestures.
`rotate`
  Two finger gesture to simulate a rotate.

Gesture can be simulated by calling `simulateGesture()` and passing the following arguments: the name of the gesture to simulate, an optional object to define gesture properties, and an optional callback function. The available properties vary per gesture.

If the location of the finger is not given, the center of the node element is used by default. This default behavior can be overridden by passing coordinates into the optional object. The coordinate values are relative to the top/left corner of the node element.

### Single Touch Gestures: Tap, Double Tab and Press

The following code simulates tap, double tap and press gestures:

    YUI().use('node-event-simulate', function(Y) {

        var node = Y.one("#myElement");

        //simulate tap gesture
        node.simulateGesture("tap");

        //simulate double-tap gesture
        node.simulateGesture("doubletap");

        //simulate press gesture
        node.simulateGesture("press", {
            hold: 3000    // press and hold for 3000ms
        });

        // simulate tap with options and callback
        node.simulateGesture("tap", {
            point: [30, 30], // tap (30, 30) relative to the top/left of the node
            hold: 3000,      // hold for 3sec in a tap
            times: 2,        // tap 2 times
            delay: 500       // delay time before next tap starts
        }, function() {
            Y.log("I was called.");
        });
    });

#### Valid Options

Optional properties for the `tap` gesture:

`point`
  Indicates the [x,y] coordinates where the tap should be simulated. Default is the center of the node element.
`hold`
  The hold time in milliseconds. This is the time between `touchstart` and `touchend` event generation.
`times`
  Indicates the number of taps. Default is 1.
`delay`
  The number of milliseconds before the next tap simulation happens. This is valid only when `times` is more than 1.

Optional properties for the `doubletap` gesture:

`point`
  Indicates the [x, y] coordinates where the doubletap should be simulated. Default is the center of the node element.

The `press` gesture is essentially a single tap with the `hold` property defined. Optional properties for the `press` gesture:

`point`
  Indicates the [x, y] coordinates where the tap should be simulated. Default is the center of the node element.
`hold`
  The hold time in milliseconds. This is the time between `touchstart` and `touchend` event generation.

### Single Touch Gestures: Move and Flick

The following code can be used To simulate various gestures of moving one finger:

    YUI().use('node-event-simulate', function(Y) {

        var node = Y.one("#myElement");

        //simulate moving a finger 200 pixels along the x-axis
        //to the right for one second (default)
        node.simulateGesture("move");

        //simulate moving a finger from the center of the node
        //to a point 70 pixels to the right and 50 pixels down over 2000ms
        node.simulateGesture("move", {
            path: {
                xdist: 70,
                ydist: -50
            } ,
            duration: 2000
        });

        //simulate a flick to the right (default)
        node.simulateGesture("flick");

        //simulate a flick down 100 pixels over 50ms
        node.simulateGesture("flick", {
            axis: y
            distance: -100
            duration: 50
        });

    });

#### Valid Options

Optional properties for the `move` gesture:

`path`
  Indicates the path of the finger movement. It's an object with three optional properties: `point`, `xdist` and `ydist`. The `point` is the start point and defaults to the center of the node element. `xdist` and `ydist` indicate the distance moved in pixels along the x- and y-axis. A negative distance value indicates moving to left for `xdist` and down for `ydist`.
`duration`
  The duration of the gesture in milliseconds.

Optional properties for the `flick` gesture:

`point`
  Indicates the [x, y] coordinates where the flick should be simulated. Default is the center of the node element.
`axis`
  Valid values are either "x" or "y". Indicates moving axis. The flick moves in only 4 directions (left, right, up and down).
`distance`
  Distance to move (in pixels).
`duration`
  The duration of the gesture in milliseconds. This value may be adjusted if it is below the minimum velocity to be a flick gesture.

### Two Finger Gestures: Pinch and Rotate

The `pinch` gesture is used to simulate the pinching and spreading of two fingers. During a pinch simulation, rotation is also possible. Essentially `pinch` and `rotate` simulations share the same base implementation to allow both pinching and rotation at the same time. The only difference is `pinch` requires `start` and `end` option properties while `rotate` requires `rotation` option property.

The `pinch` and `rotate` gestures can be described as placing 2 fingers along a circle. Pinching and spreading can be described by start and end circles while rotation occurs on a single circle. If the radius of the start circle is greater than the end circle, the gesture becomes a pinch, otherwise it is a spread spread.

The following code can be used to simulate two finger gestures:

    YUI().use('node-event-simulate', function(Y) {

        var node = Y.one("#myElement");

        //simulate a pinch: "r1" and "r2" are required
        node.simulateGesture("pinch", {
            r1: 100, // start circle radius at the center of the node
            r2: 50   // end circle radius at the center of the node
        });

        //simulate a spread: same as "pinch" gesture but r2>r1
        node.simulateGesture("pinch", {
            r1: 50,
            r2: 100
        });

        //simulate rotating a node 75 degrees counter-clockwise
        node.simulateGesture("rotate", {
            rotation: -75
        });

        //simulate a pinch and a rotation at the same time.
        //fingers start on a circle of radius 100 px, placed at top/bottom
        //fingers end on a circle of radius 50px, placed at right/left
        node.simulateGesture("pinch", {
            r1: 100,
            r2: 50,
            start: 0
            rotation: 90
        });
    });

#### Valid Options

The optional properties available for `pinch` and `rotate` gestures are the same:

`center`
  The center of the circle where the two fingers are placed. Default is the center of the node element.
`r1`
  Required for `pinch` gestures but optional for `rotate`. Pixel radius of the start circle. If omitted in `rotate` gestures, default is a fourth of the node element width or height, whichever is smaller.
`r2`
  Required for `pinch` gestures but optional for `rotate` gestures. Pixel radius of the end circle. If omitted in `rotate` gestures, default is a fourth of the node element width or height, whichever is smaller.
`duration`
  The duration of the gesture in milliseconds.
`start`
  Start degree of the first finger for the rotation gesture. Default is 0 (i.e., 12:00 on a clock).
`rotation`
  Degrees to rotate from the start degree. Negative value means rotation of counter-clockwise direction.

### Gesture Simulation on iOS

If the gesture simulation is called in iOS, it generates not only touch events but also iOS specific gesture events: `gesturestart`, `gesturechange` and `gestureend`.

### Customizing Default Gesture Properties

You can define custom default behaviors for gesture simulations by modifying the following `Y.GestureSimulation.defaults` object properties:

- HOLD_TAP
- DELAY_TAP
- HOLD_PRESS
- MIN_HOLD_PRESS
- MAX_HOLD_PRESS
- DISTANCE_MOVE
- DURATION_MOVE
- MAX_DURATION_MOVE
- MIN_VELOCITY_FLICK
- DISTANCE_FLICK
- DURATION_FLICK
- MAX_DURATION_FLICK
- DURATION_PINCH

And an example:

    YUI().use('node-event-simulate', function(Y) {

        var node = Y.one("#myElement");

        Y.GestureSimulation.defaults = Y.merge(Y.GestureSimulation.defaults, {
            HOLD_TAP: 3000
        });

        //now touchend event will be generated after 3 sec from the touchstart
        //event generation.
        node.simulateGesture("tap");
    });

## Caveats and Coming Soons

### Don't use simulation in user facing code

Event simulation is for automated testing. Your application should respond to real user events. For reasons mentioned below, it can be easy to get your application into a confused runtime state when some callbacks have been executed but not others.

Typically, event simulation is sought to trigger certain callbacks. If a function needs to respond to user action or be called programmatically, it should be written accordingly and called directly in the latter case. Often a better solution is to extract the core logic from the event handler into a separate function and call that method from the event handler and from the other part of the application that was going to use simulation.

In some cases, simulation is wanted because there may be any number of subscriptions on a node, and all applicable callbacks should be triggered. If this is the case, investigate using custom events, instead.

The bottom line is, reliance on event simulation in production code is a warning sign that the architecture is not scaling. The affected code should be refactored before it becomes a larger problem.

### Only what you ask for

In many cases, events happen in groups (`mousedown`, `mouseup`, `click`, or `keydown`, `keyup`, `keypress`). If you simulate an event that is typically part of a group or is often followed by other events, the other events will NOT be generated for free.

For example, if you simulate a `click` event on a submit button, you only simulate the `click` event. The preceding `mousedown` and `mouseup`, as well as the subsequently expected 'submit' are neither simulated or fired natively.

### No synthetic event simulation yet

The Synthetic event system doesn't yet support defining simulation. In most cases, though, synthetic events are triggered by other DOM events that can be simulated, so it's often possible to trigger them by simulating the underlying events. But that ignores the point that synthetic events are supposed to mask that abstraction for your benefit.

Support for synthetic event simulation is on the roadmap.