equals( quaternion ) {

		return ( quaternion._x === this._x ) && ( quaternion._y === this._y ) && ( quaternion._z === this._z ) && ( quaternion._w === this._w );

	}
Returns `true` if this quaternion is equal with the given one.

@param {Quaternion} quaternion - The quaternion to test for equality.
@return {boolean} Whether this quaternion is equal with the given one.