Finding if three points are collinear - JavaScript

Collinear Points

Three or more points that lie on the same straight line are called collinear points.

And three points lie on the same if the slope of all three pairs of lines formed by them is equal.

Consider, for example, three arbitrary points A, B and C on a 2-D plane, they will be collinear if −

slope of AB = slope of BC = slope of accepts

Slope of a line −

The slope of a line is generally given by the tangent of the angle it makes with the positive direction of x-axis.

Alternatively, if we have two points that lie on the line, say A(x1, y1) and B(x2, y2), then the slope of line can be calculated by −

Slope of AB = (y2-y1) / (x2-x1)

Let’s write the code for this function −


Following is the code −

const a = {x: 2, y: 4};
const b = {x: 4, y: 6};
const c = {x: 6, y: 8};
const slope = (coor1, coor2) => (coor2.y - coor1.y) / (coor2.x - coor1.x);
const areCollinear = (a, b, c) => {
   return slope(a, b) === slope(b, c) && slope(b, c) === slope(c, a);
console.log(areCollinear(a, b, c));


Following is the output in the console −


Updated on: 14-Sep-2020


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