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Revision 630241 of Math.round()

• Revision slug: Web/JavaScript/Reference/Global_Objects/Math/round
• Revision title: Math.round()
• Revision id: 630241
• Created:
• Creator: quiesagua
• Is current revision? No
• Comment Revert to revision of 2014-03-18 14:48:29 by ujay68: "Last update was a translation, no an update and therefore it should be created as such."
Tags:

Revision Content

{{JSRef("Global_Objects", "Math")}}

Summary

The `Math.round()` function returns the value of a number rounded to the nearest integer.

Syntax

``Math.round(x) ``

`x`
A number.

Description

If the fractional portion of `number` is .5 or greater, the argument is rounded to the next higher integer. If the fractional portion of `number` is less than .5, the argument is rounded to the next lower integer.

Because `round` is a static method of `Math`, you always use it as `Math.round()`, rather than as a method of a `Math` object you created.

Examples

Example: Using `Math.round`

```// Returns the value 20
x = Math.round(20.49);

// Returns the value 21
x = Math.round(20.5);

// Returns the value -20
x = Math.round(-20.5);

// Returns the value -21
x = Math.round(-20.51);

// Returns the value 1 (!)
// Note the rounding error because of inaccurate floating point arithmetics
// Compare this with Math.round10(1.005, -2) from the example below
x = Math.round(1.005*100)/100;
```

Example: Decimal rounding

```// Closure
(function(){

/**
* Decimal adjustment of a number.
*
* @param	{String}	type	The type of adjustment.
* @param	{Number}	value	The number.
* @param	{Integer}	exp		The exponent (the 10 logarithm of the adjustment base).
* @returns	{Number}			The adjusted value.
*/
// If the exp is undefined or zero...
if (typeof exp === 'undefined' || +exp === 0) {
return Math[type](value);
}
value = +value;
exp = +exp;
// If the value is not a number or the exp is not an integer...
if (isNaN(value) || !(typeof exp === 'number' && exp % 1 === 0)) {
return NaN;
}
// Shift
value = value.toString().split('e');
value = Math[type](+(value[0] + 'e' + (value[1] ? (+value[1] - exp) : -exp)));
// Shift back
value = value.toString().split('e');
return +(value[0] + 'e' + (value[1] ? (+value[1] + exp) : exp));
}

// Decimal round
if (!Math.round10) {
Math.round10 = function(value, exp) {
};
}
// Decimal floor
if (!Math.floor10) {
Math.floor10 = function(value, exp) {
};
}
// Decimal ceil
if (!Math.ceil10) {
Math.ceil10 = function(value, exp) {
};
}

})();

// Round
Math.round10(55.55, -1); // 55.6
Math.round10(55.549, -1); // 55.5
Math.round10(55, 1); // 60
Math.round10(54.9, 1); // 50
Math.round10(-55.55, -1); // -55.5
Math.round10(-55.551, -1); // -55.6
Math.round10(-55, 1); // -50
Math.round10(-55.1, 1); // -60
Math.round10(1.005, -2); // 1.01 -- compare this with Math.round(1.005*100)/100 above
// Floor
Math.floor10(55.59, -1); // 55.5
Math.floor10(59, 1); // 50
Math.floor10(-55.51, -1); // -55.6
Math.floor10(-51, 1); // -60
// Ceil
Math.ceil10(55.51, -1); // 55.6
Math.ceil10(51, 1); // 60
Math.ceil10(-55.59, -1); // -55.5
Math.ceil10(-59, 1); // -50
```

Specifications

Specification Status Comment
ECMAScript 1st Edition. Implemented in JavaScript 1.0. Standard Initial definition.
{{SpecName('ES5.1', '#sec-15.8.2.15', 'Math.round')}} {{Spec2('ES5.1')}}
{{SpecName('ES6', '#sec-math.round', 'Math.round')}} {{Spec2('ES6')}}

Browser compatibility

{{CompatibilityTable}}
Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support {{CompatVersionUnknown}} {{CompatVersionUnknown}} {{CompatVersionUnknown}} {{CompatVersionUnknown}} {{CompatVersionUnknown}}
Feature Android Firefox Mobile (Gecko) IE Phone Opera Mobile Safari Mobile
Basic support {{CompatVersionUnknown}} {{CompatVersionUnknown}} {{CompatVersionUnknown}} {{CompatVersionUnknown}} {{CompatVersionUnknown}}

• {{jsxref("Math.abs()")}}
• {{jsxref("Math.ceil()")}}
• {{jsxref("Math.floor()")}}

Revision Source

```<div>
{{JSRef("Global_Objects", "Math")}}</div>
<h2 id="Summary" name="Summary">Summary</h2>
<p>The <code><strong>Math.round()</strong></code> function returns the value of a number rounded to the nearest integer.</p>
<h2 id="Syntax" name="Syntax">Syntax</h2>
<pre class="syntaxbox">
<code>Math.round(<em>x</em>) </code></pre>
<h3 id="Parameters" name="Parameters">Parameters</h3>
<dl>
<dt>
<code>x</code></dt>
<dd>
A number.</dd>
</dl>
<h2 id="Description" name="Description">Description</h2>
<p>If the fractional portion of <code>number</code> is .5 or greater, the argument is rounded to the next higher integer. If the fractional portion of <code>number</code> is less than .5, the argument is rounded to the next lower integer.</p>
<p>Because <code>round</code> is a static method of <code>Math</code>, you always use it as <code>Math.round()</code>, rather than as a method of a <code>Math</code> object you created.</p>
<h2 id="Examples" name="Examples">Examples</h2>
<h3 id="Example:_Using_Math.round" name="Example:_Using_Math.round">Example: Using <code>Math.round</code></h3>
<pre class="brush:js">
// Returns the value 20
x = Math.round(20.49);

// Returns the value 21
x = Math.round(20.5);

// Returns the value -20
x = Math.round(-20.5);

// Returns the value -21
x = Math.round(-20.51);

// Returns the value 1 (!)
// Note the rounding error because of inaccurate floating point arithmetics
// Compare this with Math.round10(1.005, -2) from the example below
x = Math.round(1.005*100)/100;
</pre>
<h3 id="Example:_Decimal_rounding" name="Example:_Decimal_rounding">Example: Decimal rounding</h3>
<pre class="brush:js">
// Closure
(function(){

/**
* Decimal adjustment of a number.
*
* @param	{String}	type	The type of adjustment.
* @param	{Number}	value	The number.
* @param	{Integer}	exp		The exponent (the 10 logarithm of the adjustment base).
* @returns	{Number}			The adjusted value.
*/
// If the exp is undefined or zero...
if (typeof exp === 'undefined' || +exp === 0) {
return Math[type](value);
}
value = +value;
exp = +exp;
// If the value is not a number or the exp is not an integer...
if (isNaN(value) || !(typeof exp === 'number' &amp;&amp; exp % 1 === 0)) {
return NaN;
}
// Shift
value = value.toString().split('e');
value = Math[type](+(value[0] + 'e' + (value[1] ? (+value[1] - exp) : -exp)));
// Shift back
value = value.toString().split('e');
return +(value[0] + 'e' + (value[1] ? (+value[1] + exp) : exp));
}

// Decimal round
if (!Math.round10) {
Math.round10 = function(value, exp) {
};
}
// Decimal floor
if (!Math.floor10) {
Math.floor10 = function(value, exp) {
};
}
// Decimal ceil
if (!Math.ceil10) {
Math.ceil10 = function(value, exp) {
};
}

})();

// Round
Math.round10(55.55, -1); // 55.6
Math.round10(55.549, -1); // 55.5
Math.round10(55, 1); // 60
Math.round10(54.9, 1); // 50
Math.round10(-55.55, -1); // -55.5
Math.round10(-55.551, -1); // -55.6
Math.round10(-55, 1); // -50
Math.round10(-55.1, 1); // -60
Math.round10(1.005, -2); // 1.01 -- compare this with Math.round(1.005*100)/100 above
// Floor
Math.floor10(55.59, -1); // 55.5
Math.floor10(59, 1); // 50
Math.floor10(-55.51, -1); // -55.6
Math.floor10(-51, 1); // -60
// Ceil
Math.ceil10(55.51, -1); // 55.6
Math.ceil10(51, 1); // 60
Math.ceil10(-55.59, -1); // -55.5
Math.ceil10(-59, 1); // -50
</pre>
<h2 id="Specifications">Specifications</h2>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">Specification</th>
<th scope="col">Status</th>
<th scope="col">Comment</th>
</tr>
<tr>
<td>ECMAScript 1st Edition. Implemented in JavaScript 1.0.</td>
<td>Standard</td>
<td>Initial definition.</td>
</tr>
<tr>
<td>{{SpecName('ES5.1', '#sec-15.8.2.15', 'Math.round')}}</td>
<td>{{Spec2('ES5.1')}}</td>
<td>&nbsp;</td>
</tr>
<tr>
<td>{{SpecName('ES6', '#sec-math.round', 'Math.round')}}</td>
<td>{{Spec2('ES6')}}</td>
<td>&nbsp;</td>
</tr>
</tbody>
</table>
<h2 id="Browser_compatibility">Browser compatibility</h2>
<div>
{{CompatibilityTable}}</div>
<div id="compat-desktop">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Chrome</th>
<th>Firefox (Gecko)</th>
<th>Internet Explorer</th>
<th>Opera</th>
<th>Safari (WebKit)</th>
</tr>
<tr>
<td>Basic support</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
</tr>
</tbody>
</table>
</div>
<div id="compat-mobile">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Android</th>
<th>Firefox Mobile (Gecko)</th>
<th>IE Phone</th>
<th>Opera Mobile</th>
<th>Safari Mobile</th>
</tr>
<tr>
<td>Basic support</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
</tr>
</tbody>
</table>
</div>