EN
JavaScript - Math.round() method example
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Math round is a static method that returns a number that is rounded to the closest integer number.
// ONLINE-RUNNER:browser;
console.log( Math.round( 5 ) ); // 5
console.log( Math.round( 2.49 ) ); // 2
console.log( Math.round( 2.50 ) ); // 3
console.log( Math.round( 2.51 ) ); // 3
console.log( Math.round( -2.49 ) ); // -2
console.log( Math.round( -2.50 ) ); // -2
console.log( Math.round( -2.51 ) ); // -3
console.log( Math.round( 0.999 ) ); // 1
console.log( Math.round( 1.001 ) ); // 1
console.log( Math.round( -1.001 ) ); // -1
1. Documentation
| Syntax | Math.round(number) |
| Parameters | number - integer or float number value (primitive value). |
| Result | Rounded number value (primitive value). |
| Description | round is a static method that returns a number that is rounded to the closest integer number. |
2. Custom round method examples
2.1. Rounding with precision to n places example
This section contains a custom function that shows how to round numbers with precision to n places.
// ONLINE-RUNNER:browser;
function roundPrecised(number, precision) {
var power = Math.pow(10, precision);
return Math.round(number * power) / power;
}
// Usage example:
console.log( roundPrecised( 5 , 0 ) ); // 5
console.log( roundPrecised( 5. , 0 ) ); // 5
console.log( roundPrecised( .5, 0 ) ); // 1
console.log( roundPrecised( 1.2345, 0 ) ); // 1
console.log( roundPrecised( 1.2345, 1 ) ); // 1.2
console.log( roundPrecised( 1.2345, 2 ) ); // 1.23
console.log( roundPrecised( 1.2345, 3 ) ); // 1.235
console.log( roundPrecised( -1.2345, 0 ) ); // -1
console.log( roundPrecised( -1.2345, 1 ) ); // -1.2
console.log( roundPrecised( -1.2345, 2 ) ); // -1.23
console.log( roundPrecised( -1.2345, 3 ) ); // -1.234
console.log( roundPrecised( 12345, -1 ) ); // 12350
console.log( roundPrecised( 12345, -2 ) ); // 12300
console.log( roundPrecised( 12345, -3 ) ); // 12000
2.2. VanillaJS round implementation example
This section contains custom round function implementation.
// ONLINE-RUNNER:browser;
function roundNumber(value) {
if (value < 0.0) {
var rest = (value % 1.0);
if(rest < -0.5) {
rest += 1.0;
}
return value - rest;
} else {
value += 0.5;
return value - (value % 1.0);
}
}
// Usage example:
console.log( roundNumber( 5 ) ); // 5
console.log( roundNumber( 2.49 ) ); // 2
console.log( roundNumber( 2.50 ) ); // 3
console.log( roundNumber( 2.51 ) ); // 3
console.log( roundNumber( 0.999 ) ); // 1
console.log( roundNumber( 1.001 ) ); // 1
console.log( roundNumber( -2.49 ) ); // -2
console.log( roundNumber( -2.50 ) ); // -2
console.log( roundNumber( -2.51 ) ); // -3
console.log( roundNumber( -1.001 ) ); // -1
3. Custom plot example
A simple plot with canvas is presented for Math.round function below.
// ONLINE-RUNNER:browser;
<!doctype html>
<html>
<head>
<style> #canvas { border: 1px solid black; } </style>
</head>
<body>
<canvas id="canvas" width="200" height="200"></canvas>
<script>
var canvas = document.querySelector('#canvas');
var context = canvas.getContext('2d');
// cosine chart range
var x1 = -10.0;
var x2 = +10.0;
var y1 = -10.0;
var y2 = +10.0;
var dx = 0.01;
var xRange = x2 - x1;
var yRange = y2 - y1;
function calculatePoint(x) {
var y = Math.round(x);
// chart will be reversed horizontally 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 + '>');
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>