EN
JavaScript - Math.round() method example
8 points
Math round is a static method that returns a number that is rounded to the closest integer number.
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console.log( Math.round( 5 ) ); // 52
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console.log( Math.round( 2.49 ) ); // 24
console.log( Math.round( 2.50 ) ); // 35
console.log( Math.round( 2.51 ) ); // 36
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console.log( Math.round( -2.49 ) ); // -28
console.log( Math.round( -2.50 ) ); // -29
console.log( Math.round( -2.51 ) ); // -310
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console.log( Math.round( 0.999 ) ); // 112
console.log( Math.round( 1.001 ) ); // 113
console.log( Math.round( -1.001 ) ); // -1| 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. |
This section contains a custom function that shows how to round numbers with precision to n places.
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function roundPrecised(number, precision) {2
var power = Math.pow(10, precision);3
return Math.round(number * power) / power;4
}5
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// Usage example:8
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console.log( roundPrecised( 5 , 0 ) ); // 510
console.log( roundPrecised( 5. , 0 ) ); // 511
console.log( roundPrecised( .5, 0 ) ); // 112
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console.log( roundPrecised( 1.2345, 0 ) ); // 114
console.log( roundPrecised( 1.2345, 1 ) ); // 1.215
console.log( roundPrecised( 1.2345, 2 ) ); // 1.2316
console.log( roundPrecised( 1.2345, 3 ) ); // 1.23517
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console.log( roundPrecised( -1.2345, 0 ) ); // -119
console.log( roundPrecised( -1.2345, 1 ) ); // -1.220
console.log( roundPrecised( -1.2345, 2 ) ); // -1.2321
console.log( roundPrecised( -1.2345, 3 ) ); // -1.23422
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console.log( roundPrecised( 12345, -1 ) ); // 1235024
console.log( roundPrecised( 12345, -2 ) ); // 1230025
console.log( roundPrecised( 12345, -3 ) ); // 12000This section contains custom round function implementation.
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function roundNumber(value) {2
if (value < 0.0) {3
var rest = (value % 1.0);4
if(rest < -0.5) {5
rest += 1.0;6
}7
return value - rest;8
} else {9
value += 0.5;10
return value - (value % 1.0);11
}12
}13
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// Usage example:16
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console.log( roundNumber( 5 ) ); // 518
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console.log( roundNumber( 2.49 ) ); // 220
console.log( roundNumber( 2.50 ) ); // 321
console.log( roundNumber( 2.51 ) ); // 322
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console.log( roundNumber( 0.999 ) ); // 124
console.log( roundNumber( 1.001 ) ); // 125
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console.log( roundNumber( -2.49 ) ); // -227
console.log( roundNumber( -2.50 ) ); // -228
console.log( roundNumber( -2.51 ) ); // -329
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console.log( roundNumber( -1.001 ) ); // -1A simple plot with canvas is presented for Math.round function below.
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<html>3
<head>4
<style> #canvas { border: 1px solid black; } </style>5
</head>6
<body>7
<canvas id="canvas" width="200" height="200"></canvas>8
<script>9
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var canvas = document.querySelector('#canvas');11
var context = canvas.getContext('2d');12
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// cosine chart range14
var x1 = -10.0;15
var x2 = +10.0;16
var y1 = -10.0;17
var y2 = +10.0;18
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var dx = 0.01;20
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var xRange = x2 - x1;22
var yRange = y2 - y1;23
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function calculatePoint(x) {25
var y = Math.round(x);26
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// chart will be reversed horizontally because of reversed canvas pixels28
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var nx = (x - x1) / xRange; // normalized x30
var ny = 1.0 - (y - y1) / yRange; // normalized y31
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var point = {33
x: nx * canvas.width,34
y: ny * canvas.height35
};36
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return point;38
}39
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console.log('x range: <' + x1 + '; ' + x2 + '>');41
console.log('y range: <' + y1 + '; ' + y2 + '>');42
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var point = calculatePoint(x1);44
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context.beginPath();46
context.moveTo(point.x, point.y);47
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for (var x = x1 + dx; x < x2; x += dx) {49
point = calculatePoint(x);50
context.lineTo(point.x, point.y);51
}52
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point = calculatePoint(x2);54
context.lineTo(point.x, point.y);55
context.stroke();56
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</script>58
</body>59
</html>