EN
JavaScript - Math.atan() method example
16
points
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.
// ONLINE-RUNNER:browser;
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
1. Documentation
| Syntax | Math.atan(number) |
| Parameters |
|
| Result |
If value can not be calculated |
| Description |
|
2. Working with degrees
// ONLINE-RUNNER:browser;
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
3. Canvas plot example
// ONLINE-RUNNER:browser;
<!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>