Basic Vector2 JavaScript Math Helper Class

Vector2.js

function Vector2(x, y) {
	this.x = (x === undefined) ? 0 : x;
	this.y = (y === undefined) ? 0 : y;
}

Vector2.prototype = {
	set: function(x, y) {
		this.x = x || 0;
		this.y = y || 0;
	},

	clone: function() {
		return new Vector2(this.x, this.y)
	},

	add: function(vector) {
		return new Vector2(this.x + vector.x, this.y + vector.y);
	},

	subtract: function(vector) {
		return new Vector2(this.x - vector.x, this.y - vector.y);
	},

	scale: function(scalar) {
		return new Vector2(this.x * scalar, this.y * scalar);
	},

	dot: function(vector) {
		return (this.x * vector.x + this.y + vector.y);
	},

	moveTowards: function(vector, t) {
		// Linearly interpolates between vectors A and B by t.
		// t = 0 returns A, t = 1 returns B
		t = Math.min(t, 1); // still allow negative t
		var diff = vector.subtract(this);
		return this.add(diff.scale(t));
	},

	magnitude: function() {
		return Math.sqrt(this.magnitudeSqr());
	},

	magnitudeSqr: function() {
		return (this.x * this.x + this.y * this.y);
	},

	distance: function (vector) {
		return Math.sqrt(this.distanceSqr(vector));
	},

	distanceSqr: function (vector) {
		var deltaX = this.x - vector.x;
		var deltaY = this.y - vector.y;
		return (deltaX * deltaX + deltaY * deltaY);
	},

	normalize: function() {
		var mag = this.magnitude();
		var vector = this.clone();
		if(Math.abs(mag) < 1e-9) {
			vector.x = 0;
			vector.y = 0;
		} else {
			vector.x /= mag;
			vector.y /= mag;
		}
		return vector;
	},

	angle: function() {
		return Math.atan2(this.y, this.x);
	},

	rotate: function(alpha) {
		var cos = Math.cos(alpha);
		var sin = Math.sin(alpha);
		var vector = new Vector2();
		vector.x = this.x * cos - this.y * sin;
		vector.y = this.x * sin + this.y * cos;
		return vector;
	},

	toPrecision: function(precision) {
		var vector = this.clone();
		vector.x = vector.x.toFixed(precision);
		vector.y = vector.y.toFixed(precision);
		return vector;
	},

	toString: function () {
		var vector = this.toPrecision(1);
		return ("[" + vector.x + "; " + vector.y + "]");
	}
};

dot: function(vector) {
return (this.x * vector.x + this.y* vector.y);
}
:)

I think there's a bug in toPrecision. The code vector.[x|y].toFixed(precision) returns a string. It should be a number.
vector.x = Number(vector.x.toFixed(precision); and the same for "y".

Also, you should use const instead of var, especially since this class is so immutable.

How does (x === undefined) ? 0 : x; work? How does x || 0; work? Why is one used in function Vector2 and another used in set?

I think there's a bug in toPrecision. The code vector.[x|y].toFixed(precision) returns a string. It should be a number.
vector.x = Number(vector.x.toFixed(precision); and the same for "y".

Also, you should use const instead of var, especially since this class is so immutable.

That's actually supposed to be a string
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toFixed

toFixed() returns a string representation of numObj that does not use exponential notation and has exactly digits digits after the decimal place.

How does (x === undefined) ? 0 : x; work? How does x || 0; work? Why is one used in function Vector2 and another used in set?

This is Javascript's ternary operator. It's basically an if-statement compressed onto a single expression.
The format is boolean?value1:value2, value1 is returned when boolean is true, elsewise return value2.

Hey, I know this discussion it's kinda dead, but I kinda "improved" this code (just documented and add some new nice functions) :)

(@Dalimil) If you/any one want to update/use the code, it's OK, I am happy to help: https://gitlab.com/201flaviosilva/utilsjs/-/blob/2b165a247e22cd22cb38dae11d0da1819b741303/src/Vector2.js

(Any problem/but/etc... pls report 😅 )

Just lost so much time because of a bug in this code.... Dot is implemented as:

dot: function(vector) {
     return (this.x * vector.x + this.y + vector.y);
},

but should be:

dot: function(vector) {
     return (this.x * vector.x + this.y * vector.y);
},