マルチタッチ検出

window.addEventListener('load', (event) => {
    let e: HTMLElement | null = document.querySelector('#canvas-wrapper canvas');

    ["touchstart", "touchmove", "touchend"].forEach((type: any) => {
        if (!e) return;
        e.addEventListener(type, (event: TouchEvent) => {
            event.preventDefault();
            let e: HTMLElement | null = document.querySelector('#info');
            let s: string = '';
    
            if(!e) return;
    
            e.innerHTML = '';
            for (var i = 0; i < event.touches.length; i++) {
                var t = event.touches[i];
                s += "[" + i + "]";
                s += "x=" + t.pageX + ",";
                s += "y=" + t.pageY + "<br>";
            }
            e.innerHTML = s;
        }, { passive: false });
    })
})