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Revision 363841 of Math.round()

  • Revision slug: JavaScript/Reference/Global_Objects/Math/round
  • Revision title: Math.round
  • Revision id: 363841
  • Created:
  • Creator: haasz
  • Is current revision? No
  • Comment Good tips decimal rounding (tested).

Revision Content

Summary

Returns the value of a number rounded to the nearest integer.

Method of Math
Implemented in JavaScript 1.0
ECMAScript Edition ECMAScript 1st Edition

Syntax

Math.round(x) 

Parameters

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)

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.
	 */
	function decimalAdjust(type, value, exp) {
		// 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) {
			return decimalAdjust('round', value, exp);
		};
	}
	// Decimal floor
	if (!Math.floor10) {
		Math.floor10 = function(value, exp) {
			return decimalAdjust('floor', value, exp);
		};
	}
	// Decimal ceil
	if (!Math.ceil10) {
		Math.ceil10 = function(value, exp) {
			return decimalAdjust('ceil', 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
// 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

See also

Revision Source

<h2 id="Summary" name="Summary">Summary</h2>
<p>Returns the value of a number rounded to the nearest integer.</p>
<table class="standard-table">
  <thead>
    <tr>
      <th class="header" colspan="2">Method of <a href="/en-US/docs/JavaScript/Reference/Global_Objects/Math"><code>Math</code></a></th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>Implemented in</td>
      <td>JavaScript 1.0</td>
    </tr>
    <tr>
      <td>ECMAScript Edition</td>
      <td>ECMAScript 1st Edition</td>
    </tr>
  </tbody>
</table>
<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)</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.
	 */
	function decimalAdjust(type, value, exp) {
		// 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) {
			return decimalAdjust('round', value, exp);
		};
	}
	// Decimal floor
	if (!Math.floor10) {
		Math.floor10 = function(value, exp) {
			return decimalAdjust('floor', value, exp);
		};
	}
	// Decimal ceil
	if (!Math.ceil10) {
		Math.ceil10 = function(value, exp) {
			return decimalAdjust('ceil', 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
// 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="See_also" name="See_also">See also</h2>
<ul>
  <li><a href="/en-US/docs/JavaScript/Reference/Global_Objects/Math/abs">Math.abs</a></li>
  <li><a href="/en-US/docs/JavaScript/Reference/Global_Objects/Math/ceil">Math.ceil</a></li>
  <li><a href="/en-US/docs/JavaScript/Reference/Global_Objects/Math/floor">Math.floor</a></li>
</ul>
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	"fr": "fr/R\u00e9f\u00e9rence_de_JavaScript_1.5_Core/Objets_globaux/Math/round"
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