EN
JavaScript - Math.cos() method example
15
points
The Math.cos() function returns the cosine of the specified angle in radians in the range -1 to +1.
// ONLINE-RUNNER:browser;
console.log( Math.cos( 0 ) ); // 1 <- 0 degrees
console.log( Math.cos( 1.5707963267948966 ) ); // ~0 <- ~90 degrees == PI / 2
console.log( Math.cos( 3.1415926535897932 ) ); // ~-1 <- ~180 degrees == PI
console.log( Math.cos( 4.71238898038469 ) ); // ~0 <- ~270 degrees == -PI * (3 / 2)
console.log( Math.cos( 6.2831853071795850 ) ); // ~1 <- ~360 degrees == PI * 2
console.log( Math.cos(-1.5707963267948966 ) ); // ~0 <- ~-90 degrees == -PI / 2
Note:
6.123233995736766e-17,-1.8369701987210297e-16and6.123233995736766e-17should be equal to0but they are not because of computation precision error.
1. Documentation
| Syntax | Math.cos(number) |
| Parameters | number - integer or float number value in radians (primitive value). |
| Result |
returns a numeric value between |
| Description | cos is static method that takes only one parameter and returns approximation of cos(x) mathematical function result. |
2. Working with radians
// ONLINE-RUNNER:browser;
var x1 = 0.0; // beginning of calculation in radians
var x2 = Math.PI / 2; // ending of calculation radians
var dx = Math.PI / 36; // calculation step in degrees
for (var rad = x1; rad <= x2; rad += dx) {
var y = Math.cos(rad);
console.log('cos(' + rad + ' rad) = ' + y);
}
3. Working with degrees
// ONLINE-RUNNER:browser;
function calculateCos(deg) {
var rad = (Math.PI / 180) * deg;
return Math.cos(rad);
}
// Usage example:
var x1 = 0.0; // beginning of calculation in degrees
var x2 = 90.0; // ending of calculation degrees
var dx = 5.0; // calculation step in degrees
for (var deg = x1; deg <= x2; deg += dx) {
var y = calculateCos(deg );
console.log('cos(' + deg + ' deg) = ' + y);
}
4. Reversed console plot example
// ONLINE-RUNNER:browser;
var x1 = 0.0; // beginning of cosine chart
var x2 = 6 * 3.14 // end of cosine chart
var dx = 3.14 / 4.0; // x axis step
var dy = 1.0 / 5.0; // y axis step
for (var rad = x1; rad < x2; rad += dx) {
var y1 = 0.0;
var y2 = Math.cos(rad) + 1;
var line = '';
for(var y = y1; y < y2; y += dy) {
line += ' ';
}
console.log(line + '+');
}
5. 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="130"></canvas>
<script>
function Chart(canvas, x1, x2, y1, y2, dx, func) {
var self = this;
var context = canvas.getContext('2d');
var width = canvas.width;
var height = canvas.height;
var xRange = x2 - x1;
var yRange = y2 - y1;
var calculatePoint = function(x) {
var y = func(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
return {
x: nx * width,
y: ny * height
};
};
self.drawChart = function() {
var point = calculatePoint(x1);
context.beginPath();
context.moveTo(point.x, point.y);
for (var x = x1 + dx; x < x2; x += dx) {
var point = calculatePoint(x);
context.lineTo(point.x, point.y);
}
var point = calculatePoint(x2);
context.lineTo(point.x, point.y);
context.stroke();
};
};
// Usage example:
var canvas = document.querySelector('#canvas');
// cosine chart range
var x1 = 0; // 0 degress
var x2 = +2 * Math.PI; // +360 degress
var y1 = -1.0;
var y2 = +1.0;
var dx = 0.1;
var chart = new Chart(canvas, x1, x2, y1, y2, dx, Math.cos);
chart.drawChart();
console.log('x range: <' + x1 + '; ' + x2 + '> // angles in radians');
console.log('y range: <' + y1 + '; ' + y2 + '>');
</script>
</body>
</html>