Checking for straight lines in JavaScript

We need to write a JavaScript function that takes an array of coordinate pairs and determines if all points form a straight line. Each subarray contains exactly two items representing x and y coordinates.

Our function checks whether the coordinates form a straight line by calculating and comparing slopes between points.

For example:

[[4, 5], [5, 6]] should return true (slope = 1)
[[1, 2], [2, 3], [4, 5]] should return true (all have slope = 1)
[[1, 1], [2, 2], [3, 4]] should return false (different slopes)

The array is guaranteed to contain at least two coordinate pairs.

Algorithm

To check if points form a straight line, we calculate the slope between the first point and every other point. If all slopes are equal, the points are collinear.

The slope formula is: slope = (y2 - y1) / (x2 - x1)

Example

const coordinates = [
    [4, 5],
    [5, 6],
    [6, 7]
];

const checkStraightLine = (coordinates = []) => {
    if (coordinates.length 

Test 1: true
Test 2: false
Test 3: true


Handling Vertical Lines

For vertical lines (where x coordinates are the same), we use Infinity to represent the undefined slope:

const verticalLine = [[2, 1], [2, 3], [2, 5]];
console.log("Vertical line test:", checkStraightLine(verticalLine));

const mixedPoints = [[2, 1], [3, 2], [2, 5]]; // Not a straight line
console.log("Mixed points test:", checkStraightLine(mixedPoints));


Vertical line test: true
Mixed points test: false


How It Works

The algorithm works by:


Taking the first two points as reference to calculate the expected slope
For each remaining point, calculating its slope with the first point
If any slope differs from the reference slope, the points don't form a straight line
Special handling for vertical lines using Infinity



Conclusion

This solution efficiently determines if coordinate points form a straight line by comparing slopes. It handles both regular and vertical lines correctly with O(n) time complexity.