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

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

Quick solution:

function rotateLeft(vector) {
  	var a = vector.a;
  	var b = vector.b;
  	return {
      	a: { x: -a.y, y: a.x },  // check: https://dirask.com/posts/1GoW61
      	b: { x: -b.y, y: b.x }
    };
}

var vector1 = {a: {x: 1, y: 2}, b: {x: 2, y: 4}};  // vector [A1, B1] = ( 1, 2) -> ( 2, 4)
var vector2 = rotateLeft(vector1);                 // vector [A2, B2] = (-2, 1) -> (-4, 2)

Rotation preview:

Practical example

// ONLINE-RUNNER:browser;

function rotateLeft(vector) {
  	var a = vector.a;
  	var b = vector.b;
  	return {
      	a: { x: -a.y, y: a.x },  // check: https://dirask.com/posts/1GoW61
      	b: { x: -b.y, y: b.x }
    };
}


// Helper methods:

function printPoint(point) {
	return '(' + point.x + ', ' + point.y + ')';
}

function printVector(name, vector) {
  	console.log(name + ': ' + printPoint(vector.a) + ' -> ' + printPoint(vector.b));
}


// Usage example:
                                  // direction:
var vector1 = {                   //   ↑
	a: {x: 0, y: 1},              // a = beginning point
  	b: {x: 0, y: 2}               // b = ending point (arrow/head)
};          

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

printVector('vector1', vector1);  // ( 0,  1) -> ( 0,  2)  ↑
printVector('vector2', vector2);  // (-1,  0) -> (-2,  0)  ←
printVector('vector3', vector3);  // ( 0, -1) -> ( 0, -2)  ↓
printVector('vector4', vector4);  // ( 1,  0) -> ( 2,  0)  →

See also

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

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

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