我今天有兩個放大縮小按鈕，想讓user按放大時用js把一個100x72的圖片 以寬為主每次加4px等比放大，反之亦然，但不知道小數位數該如何取才能正確控制高度 等比放大的公式為
I have two button to let user enlarge or reduce a 100px x 72px image immediately on the page, 4px enlarge or reduce one time by width, but I don't know how to control the height to make resize proportionally. resize formula is below: enlarge (height/width)*(width+4) reduce (height/width)*(width-4) I try to use xnview software to get the resize information, you can see, the height will not resize proportionally after few clicks, for example, if I click reduce 10 times, and click enlarge 10 times, the image should be origin size 100x72, but it's not, how to do it right? xnview reduce 100 72 96 69 92 66 88 63 84 60 80 58 76 55 JS reduce 100 72 96 69.12 92 66.125 88 63.130434782608695 84 60.13636363636364 80 57.142857142857146 76 54.15 xnview enlarge 100 72 104 75 108 78 112 81 116 84 120 86 124 89 JS enlarge 100 72 104 74.88 108 77.88461538461539 112 80.88888888888889 116 83.89285714285714 120 86.89655172413794 124 89.89999999999999
