Passive events support

passive-events-detect.js

// https://github.com/Modernizr/Modernizr/issues/1894#issuecomment-198035521

window.passiveEventsSupport = function passiveEventsSupport() {
    if (passiveEventsSupport.supportsPassive !== undefined) {
        return passiveEventsSupport.supportsPassive
    }

    var supportsPassive = false
    var opts = Object.defineProperty && Object.defineProperty({}, 'passive', {
            get: function () {
                supportsPassive = true
            }
        })

    document.addEventListener('test', function() {}, opts)

    passiveEventsSupport.supportsPassive = supportsPassive
}

// ******
// Using
// Use our detect's results. passive applied if supported, capture will be false either way.
elem.addEventListener('touchstart', fn, passiveEventsSupport() ? { passive: true } : false);