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# 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>
<style> #canvas { border: 1px solid black; } </style>
<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>

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