js运动函数

function doMove ( obj, attr, dir, target, callback ) {

	dir = parseInt(getStyle( obj, attr )) < target ? dir : -dir;

	clearInterval( obj.timer );

	obj.timer = setInterval(function () {

		var speed = parseInt(getStyle( obj, attr )) + dir;			// 步长

		if ( speed > target && dir > 0 ||  speed < target && dir < 0  ) {
			speed = target;
		}

		obj.style[attr] = speed + ‘px‘;

		if ( speed == target ) {
			clearInterval( obj.timer );

			callback && callback();

		}

	}, 30);
}

function getStyle ( obj, attr ) { return obj.currentStyle?obj.currentStyle[attr] : getComputedStyle( obj )[attr]; }