比例尺寸计算

zoomSize.js

/**
 * 比例尺寸计算
 * 
 * @param options
 * @param options.w 
 * @param options.h
 * @param [options.newW]
 * @param [options.newH]
 * @param [options.max]
 * @returns {object}
 */
function zoomSize(options) {
  var w = options.w
            var h = options.h
            var newW = options.newW
            var newH = options.newH
            var max = options.max
            var result = {w:w,h:h}

            if(newW && newH) {
                return result
            }
            else if (max) {
                return w > h 
                          ? zoomSize({w:w, h:h, newW: max}) 
                          : zoomSize({w:w, h:h, newH: max})
            }
            else if(newW) {
                result.w =newW
                result.h = h * (newW / w)
            }
            else if (newH) {
                result.w = w * (newH / h)
                result.h = newH
            }

            return {
                w: Math.ceil(result.w),
                h: Math.ceil(result.h)
            }
}

console.log(zoomSize({
    w:180,
    h:400,
    newW:660
}))