在javascript中将图像划分为相等的部分

I've been working on dividing up a dartboard image (646px X 646px) into sections. Firstly I have the radian information for each slice on this image (0.314 Radians (360 degrees/20 slices = 18 degrees ) ), the exact x and y values of the centre of the dartboard image and now a lookup table containing the start and end radians for each slice along with the score - i.e. score 20, start 0, end 0.314. Does anyone have any tips on how to proceed with how to detect mouseclick/key-down events in regards to what section i'm selecting? i.e. how would the board know if I'm selecting the 20 slice?I've been working on dividing up a dartboard im