# Checking for straight lines in JavaScript

JavascriptWeb DevelopmentFront End TechnologyObject Oriented Programming

We are required to write a JavaScript function that takes in an array of arrays. Each subarray will contain exactly two items, representing the x and y coordinates respectively.

Our function should check whether or not the coordinates specified by these subarrays form a straight line.

For example −

[[4, 5], [5, 6]] should return true.

The array is guaranteed to contain at least two subarrays.

## Example

The code for this will be −

const coordinates = [
[4, 5],
[5, 6]
];
const checkStraightLine = (coordinates = []) => {
if(coordinates.length === 0) return false;
let x1 = coordinates;
let y1 = coordinates;
let slope1 = null;
for(let i=1;i<coordinates.length;i++){
let x2= coordinates[i];
let y2= coordinates[i];
if(x2-x1 === 0){
return false;
}
if(slope1 === null){
slope1 = (y2-y1) / (x2-x1);
continue;
}
let slope2 = (y2-y1) / (x2-x1);
if(slope2 != slope1){
return false;
}
}
return true;
};
console.log(checkStraightLine(coordinates));

## Explanation

We determine the slope for each point with the first point if the slope is equal, it’s a straight line, otherwise if one of the points have different slope this means, points are not on the same line.

## Output

And the output in the console will be −

true