ionic-framework/ionic/gestures/slide-edge-gesture.js

import {SlideGesture} from 'ionic/gestures/slide-gesture';
import * as util from 'ionic/util';

export class SlideEdgeGesture extends SlideGesture {
  constructor(element: Element, opts: Object = {}) {
    util.defaults(opts, {
      edge: 'left',
      threshold: 50
    });
    super(element, opts);
    // Can check corners through use of eg 'left top'
    this.edges = opts.edge.split(' ');
    this.threshold = opts.threshold;
  }

  canStart(ev) {
    this._containerRect = this.getContainerDimensions();
    return this.edges.every(edge => this._checkEdge(edge, ev.gesture.center));
  }

  getContainerDimensions() {
    return {
      left: 0,
      top: 0,
      width: window.innerWidth,
      height: window.innerHeight
    };
  }

  _checkEdge(edge, pos) {
    switch(edge) {
      case 'left': return pos.x <= this._containerRect.left + this.threshold;
      case 'right': return pos.x >= this._containerRect.width - this.threshold;
      case 'top': return pos.y <= this._containerRect.top + this.threshold;
      case 'bottom': return pos.y >= this._containerRect.height - this.threshold;
    }
  }

}