 <p>normally you use Number() or parseInt("", [radix]) to parse a string into a real number.</p> <p>I am guessing you are asking about what happens when the string you parse is above the int - threshold. in this case it greatly depends on what you are trying to accomplish. </p> <p>There are some libraries that allow working with big numbers such as <a href="http://www.leemon.com/crypto/BigInt.js" rel="nofollow noreferrer">http://www.leemon.com/crypto/BigInt.js</a> (did not test it, but it looks ok). Also try searching for BigInt javascript or BigMath.</p> <p>In short: working with VERY large number or exact decimals is a challenge in every programming language and often requires very specific mathematical libraries (which are less convenient and often a lot slower then when you work in "normal" (int/long) areas) - which obviously is not an issue when you REALLY want those big numbers.</p>