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copied!<p>1.2 + 1.1 may be ok but 0.2 + 0.1 may not be ok.</p> <p>This is a problem in virtually every language that is in use today. The problem is that 1/10 cannot be accurately represented as a binary fraction just like 1/3 cannot be represented as a decimal fraction.</p> <p>The workarounds include rounding to only the number of decimal places that you need and either work with strings, which are accurate:</p> <pre><code>(0.2 + 0.1).toFixed(4) === 0.3.toFixed(4) // true </code></pre> <p>or you can convert it to numbers after that:</p> <pre><code>+(0.2 + 0.1).toFixed(4) === 0.3 // true </code></pre> <p>or using Math.round:</p> <pre><code>Math.round(0.2 * X + 0.1 * X) / X === 0.3 // true </code></pre> <p>where <code>X</code> is some power of 10 e.g. 100 or 10000 - depending on what precision you need.</p> <p>Or you can use cents instead of dollars when counting money:</p> <pre><code>cents = 1499; // $14.99 </code></pre> <p>That way you only work with integers and you don't have to worry about decimal and binary fractions at all.</p> <h2>2017 Update</h2> <p>The situation of representing numbers in JavaScript may be a little bit more complicated than it used to. It <strong>used to be the case</strong> that we had only one numeric type in JavaScript:</p> <ul> <li>64-bit floating point (the <a href="https://en.wikipedia.org/wiki/IEEE_754-1985#Double-precision_64_bit" rel="nofollow noreferrer">IEEE 754 double precision floating-point number</a> - see: <a href="http://www.ecma-international.org/ecma-262/5.1/index.html#sec-8.5" rel="nofollow noreferrer">ECMA-262 Edition 5.1, Section 8.5</a> and <a href="http://www.ecma-international.org/ecma-262/6.0/index.html#sec-ecmascript-language-types-number-type" rel="nofollow noreferrer">ECMA-262 Edition 6.0, Section 6.1.6</a>)</li> </ul> <p><strong>This is no longer the case</strong> - not only there are currently more numerical types in JavaScript today, more are on the way, including a proposal to add arbitrary-precision integers to ECMAScript, and hopefully, arbitrary-precision decimals will follow - see this answer for details:</p> <ul> <li><a href="https://stackoverflow.com/questions/5179836/difference-between-floats-and-ints-in-javascript/5179886#5179886">Difference between floats and ints in Javascript?</a></li> </ul> <h2>See also</h2> <p>Another relevant answer with some examples of how to handle the calculations:</p> <ul> <li><a href="https://stackoverflow.com/questions/44949148/node-giving-strange-output-on-sum-of-particular-float-digits/44949594#44949594">Node giving strange output on sum of particular float digits</a></li> </ul>

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