JavaScript - rotate vector 2D to left direction (counterclockwise direction)

In this short article, we would like to show how to rotate any vector 2D to the left side (90 degrees) using Javascript.

Quick solution:

function rotateLeft(vector) {
	return { x: -vector.y, y: vector.x };
}

var vector1 = {x: 2, y: 4};         // vector V1 = [ 2,  4]
var vector2 = rotateLeft(vector1);  // vector V2 = [-4,  2]

Rotation preview:

Practical example

// ONLINE-RUNNER:browser;

function rotateLeft(vector) {
	return { x: -vector.y, y: vector.x };
}


// Usage example:

                                     // direction:
var vector1 = {x: 0, y: 1};          //   ↑

var vector2 = rotateLeft(vector1);   //   ←
var vector3 = rotateLeft(vector2);   //   ↓
var vector4 = rotateLeft(vector3);   //   →

console.log(vector1.x + ' ' + vector1.y);  //  0  1      ↑
console.log(vector2.x + ' ' + vector2.y);  // -1  0      ←
console.log(vector3.x + ' ' + vector3.y);  //  0 -1      ↓
console.log(vector4.x + ' ' + vector4.y);  //  1  0      →

Note: the above example works on free vectors - typical mathematical vectors that are not localised.

See also

1. JavaScript - rotate vector 2D to right direction (clockwise direction)

2. JavaScript - rotate localized vector 2D to right direction (clockwise direction)

3. JavaScript - rotate localized vector 2D to left direction (counterclockwise direction)