文本域向上滚动不工作iOS

textarea {
    overflow: auto;
    -webkit-overflow-scrolling: touch;
}

var textarea = document.querySelector('textarea');
textarea.addEventListener('touchstart', function(event) {
    this.allowScrolling = true;
    this.startY = event.touches[0].pageY;
});
textarea.addEventListener('touchmove', function(event) {
    var currentY = event.touches[0].pageY;
    var deltaY = currentY - this.startY;
    if (this.scrollHeight > this.offsetHeight) {
        if (deltaY < 0 && this.scrollTop === 0) {
            event.preventDefault();
            this.allowScrolling = false;
        } else if (deltaY > 0 && this.scrollTop + this.offsetHeight === this.scrollHeight) {
            event.preventDefault();
            this.allowScrolling = false;
        }
    } else {
        event.preventDefault();
        this.allowScrolling = false;
    }
});
textarea.addEventListener('touchend', function() {
    this.allowScrolling = true;
});