pressure/src/adapters/adapter_force_touch.js

Pressure is a lightweight JavaScript library for both Force Touch and 3D Touch through a single API.

/*
This adapter is for Macs with Force Touch trackpads.
*/
class AdapterForceTouch extends Adapter {
  constructor(el, block, options) {
    super(el, block, options);
  }

  bindEvents() {
    this.add('webkitmouseforcewillbegin', this._startPress.bind(this));
    this.add('mousedown', this.support.bind(this));
    this.add('webkitmouseforcechanged', this.change.bind(this));
    this.add('webkitmouseforcedown', this._startDeepPress.bind(this));
    this.add('webkitmouseforceup', this._endDeepPress.bind(this));
    this.add('mouseleave', this._endPress.bind(this));
    this.add('mouseup', this._endPress.bind(this));
  }

  support(event) {
    if(this.isPressed() === false) {
      this.fail(event, this.runKey);
    }
  }

  change(event) {
    if(this.isPressed() && event.webkitForce > 0) {
      this._changePress(this.normalizeForce(event.webkitForce), event);
    }
  }

  // make the force the standard 0 to 1 scale and not the 1 to 3 scale
  normalizeForce(force) {
    return this.reachOne(map(force, 1, 3, 0, 1));
  }

  // if the force value is above 0.995 set the force to 1
  reachOne(force) {
    return force > 0.995 ? 1 : force;
  }
}