input 虚拟键盘

if (!Element.prototype.scrollIntoViewIfNeeded) {
    Element.prototype.scrollIntoViewIfNeeded = function (centerIfNeeded) {
        function withinBounds(value, min, max, extent) {
            if (false === centerIfNeeded || max <= value + extent && value <= min + extent) {
                return Math.min(max, Math.max(min, value));
            } else {
                return (min + max) / 2;
            }
        }

        function makeArea(left, top, width, height) {
            return  { "left": left, "top": top, "width": width, "height": height
                    , "right": left + width, "bottom": top + height
                    , "translate":
                        function (x, y) {
                            return makeArea(x + left, y + top, width, height);
                        }
                    , "relativeFromTo":
                        function (lhs, rhs) {
                            var newLeft = left, newTop = top;
                            lhs = lhs.offsetParent;
                            rhs = rhs.offsetParent;
                            if (lhs === rhs) {
                                return area;
                            }
                            for (; lhs; lhs = lhs.offsetParent) {
                                newLeft += lhs.offsetLeft + lhs.clientLeft;
                                newTop += lhs.offsetTop + lhs.clientTop;
                            }
                            for (; rhs; rhs = rhs.offsetParent) {
                                newLeft -= rhs.offsetLeft + rhs.clientLeft;
                                newTop -= rhs.offsetTop + rhs.clientTop;
                            }
                            return makeArea(newLeft, newTop, width, height);
                        }
                    };
        }

        var parent, elem = this, area = makeArea(
            this.offsetLeft, this.offsetTop,
            this.offsetWidth, this.offsetHeight);
        while ((parent = elem.parentNode) instanceof HTMLElement) {
            var clientLeft = parent.offsetLeft + parent.clientLeft;
            var clientTop = parent.offsetTop + parent.clientTop;

            // Make area relative to parent‘s client area.
            area = area.
                relativeFromTo(elem, parent).
                translate(-clientLeft, -clientTop);

            parent.scrollLeft = withinBounds(
                parent.scrollLeft,
                area.right - parent.clientWidth, area.left,
                parent.clientWidth);

            parent.scrollTop = withinBounds(
                parent.scrollTop,
                area.bottom - parent.clientHeight, area.top,
                parent.clientHeight);

            // Determine actual scroll amount by reading back scroll properties.
            area = area.translate(clientLeft - parent.scrollLeft,
                                  clientTop - parent.scrollTop);
            elem = parent;
        }
    };
}