Source: grab_to_pan.js

/* Copyright 2013 Rob Wu <rob@robwu.nl>
 * https://github.com/Rob--W/grab-to-pan.js
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * Construct a GrabToPan instance for a given HTML element.
 * @param options.element {Element}
 * @param options.ignoreTarget {function} optional. See `ignoreTarget(node)`
 * @param options.onActiveChanged {function(boolean)} optional. Called
 *  when grab-to-pan is (de)activated. The first argument is a boolean that
 *  shows whether grab-to-pan is activated.
 */
function GrabToPan(options) {
  this.element = options.element
  this.document = options.element.ownerDocument
  if (typeof options.ignoreTarget === 'function') {
    this.ignoreTarget = options.ignoreTarget
  }
  this.onActiveChanged = options.onActiveChanged

  // Bind the contexts to ensure that `this` always points to
  // the GrabToPan instance.
  this.activate = this.activate.bind(this)
  this.deactivate = this.deactivate.bind(this)
  this.toggle = this.toggle.bind(this)
  this._onmousedown = this._onmousedown.bind(this)
  this._onmousemove = this._onmousemove.bind(this)
  this._endPan = this._endPan.bind(this)

  // This overlay will be inserted in the document when the mouse moves during
  // a grab operation, to ensure that the cursor has the desired appearance.
  const overlay = (this.overlay = document.createElement('div'))
  overlay.className = 'grab-to-pan-grabbing'
}
GrabToPan.prototype = {
  /**
   * Class name of element which can be grabbed
   */
  CSS_CLASS_GRAB: 'grab-to-pan-grab',

  /**
   * Bind a mousedown event to the element to enable grab-detection.
   * @type {() => void}
   */
  activate: function GrabToPan_activate() {
    if (!this.active) {
      this.active = true
      this.element.addEventListener('mousedown', this._onmousedown, true)
      this.element.classList.add(this.CSS_CLASS_GRAB)
      if (this.onActiveChanged) {
        this.onActiveChanged(true)
      }
    }
  },

  /**
   * Removes all events. Any pending pan session is immediately stopped.
   * @type {() => void}
   */
  deactivate: function GrabToPan_deactivate() {
    if (this.active) {
      this.active = false
      this.element.removeEventListener('mousedown', this._onmousedown, true)
      this._endPan()
      this.element.classList.remove(this.CSS_CLASS_GRAB)
      if (this.onActiveChanged) {
        this.onActiveChanged(false)
      }
    }
  },

  toggle: function GrabToPan_toggle() {
    if (this.active) {
      this.deactivate()
    } else {
      this.activate()
    }
  },

  /**
   * Whether to not pan if the target element is clicked.
   * Override this method to change the default behaviour.
   *
   * @param node {Element} The target of the event
   * @returns {boolean} Whether to not react to the click event.
   */
  ignoreTarget: function GrabToPan_ignoreTarget(node) {
    // Use matchesSelector to check whether the clicked element
    // is (a child of) an input element / link
    return node[matchesSelector](
      'a[href], a[href] *, input, textarea, button, button *, select, option'
    )
  },

  /**
   * @private
   */
  _onmousedown: function GrabToPan__onmousedown(event) {
    if (event.button !== 0 || this.ignoreTarget(event.target)) {
      return
    }
    if (event.originalTarget) {
      try {
        // eslint-disable-next-line no-unused-expressions
        event.originalTarget.tagName
      } catch (e) {
        // Mozilla-specific: element is a scrollbar (XUL element)
        return
      }
    }

    this.scrollLeftStart = this.element.scrollLeft
    this.scrollTopStart = this.element.scrollTop
    this.clientXStart = event.clientX
    this.clientYStart = event.clientY
    this.document.addEventListener('mousemove', this._onmousemove, true)
    this.document.addEventListener('mouseup', this._endPan, true)
    // When a scroll event occurs before a mousemove, assume that the user
    // dragged a scrollbar (necessary for Opera Presto, Safari and IE)
    // (not needed for Chrome/Firefox)
    this.element.addEventListener('scroll', this._endPan, true)
    event.preventDefault()
    event.stopPropagation()

    const focusedElement = document.activeElement
    if (focusedElement && !focusedElement.contains(event.target)) {
      focusedElement.blur()
    }
  },

  /**
   * @private
   */
  _onmousemove: function GrabToPan__onmousemove(event) {
    this.element.removeEventListener('scroll', this._endPan, true)
    if (isLeftMouseReleased(event)) {
      this._endPan()
      return
    }
    const xDiff = event.clientX - this.clientXStart
    const yDiff = event.clientY - this.clientYStart
    const scrollTop = this.scrollTopStart - yDiff
    const scrollLeft = this.scrollLeftStart - xDiff
    if (this.element.scrollTo) {
      this.element.scrollTo({
        top: scrollTop,
        left: scrollLeft,
        behavior: 'instant',
      })
    } else {
      this.element.scrollTop = scrollTop
      this.element.scrollLeft = scrollLeft
    }
    if (!this.overlay.parentNode) {
      document.body.appendChild(this.overlay)
    }
  },

  /**
   * @private
   */
  _endPan: function GrabToPan__endPan() {
    this.element.removeEventListener('scroll', this._endPan, true)
    this.document.removeEventListener('mousemove', this._onmousemove, true)
    this.document.removeEventListener('mouseup', this._endPan, true)
    // Note: ChildNode.remove doesn't throw if the parentNode is undefined.
    this.overlay.remove()
  },
}

// Get the correct (vendor-prefixed) name of the matches method.
let matchesSelector
;['webkitM', 'mozM', 'msM', 'oM', 'm'].some(function (prefix) {
  let name = prefix + 'atches'
  if (name in document.documentElement) {
    matchesSelector = name
  }
  name += 'Selector'
  if (name in document.documentElement) {
    matchesSelector = name
  }
  return matchesSelector // If found, then truthy, and [].some() ends.
})

// Browser sniffing because it's impossible to feature-detect
// whether event.which for onmousemove is reliable
const isNotIEorIsIE10plus = !document.documentMode || document.documentMode > 9
const chrome = window.chrome
const isChrome15OrOpera15plus = chrome && (chrome.webstore || chrome.app)
//                                         ^ Chrome 15+       ^ Opera 15+
const isSafari6plus =
  /Apple/.test(navigator.vendor) &&
  /Version\/([6-9]\d*|[1-5]\d+)/.test(navigator.userAgent)

/**
 * Whether the left mouse is not pressed.
 * @param event {MouseEvent}
 * @returns {boolean} True if the left mouse button is not pressed,
 *                    False if unsure or if the left mouse button is pressed.
 */
function isLeftMouseReleased(event) {
  if ('buttons' in event && isNotIEorIsIE10plus) {
    // http://www.w3.org/TR/DOM-Level-3-Events/#events-MouseEvent-buttons
    // Firefox 15+
    // Internet Explorer 10+
    return !(event.buttons & 1)
  }
  if (isChrome15OrOpera15plus || isSafari6plus) {
    // Chrome 14+
    // Opera 15+
    // Safari 6.0+
    return event.which === 0
  }
  return false
}

export { GrabToPan }