[Edit]

JavaScript - Math.atan() method example

1 contributors

2 contributions

0 discussions

16 points

Created by:

Welsh

902

The Math.atan function returns number in radians in the range -Math.PI/2 to +Math.PI/2. The function calculates the inverted tangent function value.

xxxxxxxxxx
 
function calculateAngle(a, b) {
    return Math.atan(a / b);
}
​
/*
  |\
  | \ h - for this function this information is not necessary
a |  \
  |__*\ <- angle
    b
*/
​
var a, b;
​
// a and b build isosceles right triangle
a = 3; 
b = a;
console.log( calculateAngle(a, b) ); // 0.7853981633974483 <- ~45 degrees
​
// a and b build half of equilateral triangle
a = 3; 
b = a * Math.sqrt(3); 
console.log( calculateAngle(a, b) ); // 0.5235987755982988 <- ~30 degrees
​
// a and b build very high (+Inf) and slim (~0) triangle
a = +Infinity; 
b = 0; 
console.log( calculateAngle(a, b) ); // 1.5707963267948966 <- ~90 degrees

Auto running

1. Documentation

Edit

Syntax	`Math.atan(number)`
Parameters	`number` - integer or float number value that represents result of operation `opposite / adjacent` on right triangle (primitive value).
Result	`number` value in radians in the range `-Math.PI/2` to `+Math.PI/2` (primitive value). If value can not be calculated `NaN` is returned.
Description	`atan` is a static method that takes only one parameter and returns an approximation of the result of the mathematical function arctangent(x).

2. Working with degrees

Edit

xxxxxxxxxx
 
function calculateAngle(a, b) {
    var angle = Math.atan(a / b);
​
    return (180 / Math.PI) * angle; // rad to deg conversion
}
​
/*
  |\
  | \ h - for this function this information is not necessary
a |  \
  |__*\ <- angle
    b
*/
​
var a, b;
​
// a an b build isosceles right triangle
a = 3; 
b = a;
console.log( calculateAngle(a, b) ); // ~45 degrees
​
// a and b build half of equilateral triangle
a = 3; 
b = a * Math.sqrt(3); 
console.log( calculateAngle(a, b) ); // ~30 degrees
​
// a and b build very high (+Inf) and slim (~0) triangle
a = +Infinity; 
b = 0; 
console.log( calculateAngle(a, b) ); // ~90 degrees

Auto running

3. Canvas plot example

Edit

xxxxxxxxxx
 
<!doctype html>
<html>
<head>
  <style> #canvas { border: 1px solid black; } </style>
</head>
<body>
  <canvas id="canvas" width="400" height="150"></canvas>
  <script>
    
    var canvas = document.querySelector('#canvas');
    var context = canvas.getContext('2d');
​
    // arctangent chart range
    var x1 = -10.0;
    var x2 = +10.0;
    var y1 = -Math.PI / 2;
    var y2 = +Math.PI / 2;
​
    var dx = 0.1;
​
    var xRange = x2 - x1;
    var yRange = y2 - y1;
​
    function calculatePoint(x) {
      var y = Math.atan(x);
​
      // chart will be reversed horizontaly because of reversed canvas pixels
​
      var nx = (x - x1) / xRange;       // normalized x
      var ny = 1.0 - (y - y1) / yRange; // normalized y
      
      var point = {
        x: nx * canvas.width,
        y: ny * canvas.height
      };
​
      return point;
    }
​
    console.log('x range: <' + x1 + '; ' + x2 + '>');
    console.log('y range: <' + y1 + '; ' + y2 + '> // angles in radians');
​
    var point = calculatePoint(x1);
    
    context.beginPath();
    context.moveTo(point.x, point.y);
​
    for (var x = x1 + dx; x < x2; x += dx) {
      point = calculatePoint(x);
      context.lineTo(point.x, point.y);
    }
​
    point = calculatePoint(x2);
    context.lineTo(point.x, point.y);
    context.stroke();
​
  </script>
</body>
</html>