JSFiddle - React, Tailwind, and code Playground

JavaScript

/*
Path:
0,0
10,10
20,10 - Angle1 to get here = 135 degrees
10,20 - Angle2 to get here = 315 degrees
*/

var point1x = 0, point1y = 0,
    point2x = 10, point2y = 10,
    point3x = 20, point3y = 10,
    point4x = 10, point4y = 20;

var slope1 = Math.atan2(point2y-point1y,point2x-point1x)*180/Math.PI;
var slope2 = Math.atan2(point3y-point2y,point3x-point2x)*180/Math.PI;
var slope3 = Math.atan2(point4y-point3y,point4x-point3x)*180/Math.PI;
alert(slope1);
alert(slope2);
alert(slope3);
var Angle1 = slope1-slope2;
var Angle2 = slope2-slope3;
alert(180-Angle1);
alert(180-Angle2);