javascript - Getting the angle from a direction vector? -

i have simple function set angle vector. gets vector's current magnitude (length), calulates angle , converts angle radians degrees. apply angle x , y, lastly multiplying vector it's original magnitude.

this.setangle = function(degree){     var l = this.length();  //magnitude of vector     var angle = degree*math.pi/180; //degress converted radians     this.x=math.cos(angle);     this.y=math.sin(angle);     this.multiply(l);  //original magnitude     return; } 

however unsure how obtain (get) angle vector. below attempt:

this.getangle = function(){     var angle = math.atan(this.y/this.x);   //radians     var degrees = angle/(180*math.pi);  //degrees     return math.floor(degrees); //round number, avoid decimal fragments } 

this attempt doesn't return value except 0 or -1.

any suggestions?

edit:

correct method:

this.getangle = function(){     var angle = math.atan2(this.y, this.x);     var degrees = 180*angle/math.pi;     return (360+math.round(degrees))%360; } 

this.getangle = function(){     var angle = math.atan2(this.y, this.x);   //radians     // need devide pi, , multiply 180:     var degrees = 180*angle/math.pi;  //degrees     return (360+math.round(degrees))%360; //round number, avoid decimal fragments }