#### Javascript - Function to calculate polygon area, Algorithm to calculate polygon area

#### Function to calculate polygon area

**Algorithm to calculate polygon area in Javascript**

function polygonArea(X, Y, numPoints) { area = 0; // Accumulates area in the loop j = numPoints-1; // The last vertex is the 'previous' one to the first for (i=0; i<numPoints; i++) { area = area + (X[j]+X[i]) * (Y[j]-Y[i]); j = i; //j is previous vertex to i } return area/2; }Where,

X, Y = Arrays of the x and y coordinates of the vertices, traced in a clockwise direction, starting at any vertex. If you trace them counterclockwise, the result will be correct but have a negative sign.

numPoints = The number of vertices

Returns = the area of the polygon

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