![]() ![]() You can polyfill Number.isNaN() using the below function: Number. On the other hand, Number.isNaN(x) returns false if x is not of type number. For example: Number( null) // 0 Number( '') // 0 Number( ' ') // 0 Number( false) // 0 Number() // false It converts a lot of surprising values to 0. Unfortunately, Number(x) is more lax when it comes to whitespace, null, and other edge cases. You might mistakenly assume this means Number(x) is safer and more strict. parseFloat() is more permissive when it comes to accepting different strings: Number( '42 fail') // NaN parseFloat( '42 fail') // 42 parseInt( '42 fail') // 42 Number( ' 10') // 10 parseFloat( ' 10') // 10 parseInt( ' 10') // 10 Number(x) and parseFloat(x) handle edge cases very differently. javascript numbers currency Share Improve this question Follow edited at 22:22 Sebastian Zartner 18.7k 10 89 132 asked at 15:46 Murtaza Mandvi 10. +( ' ') // 0 What's Wrong With Number(x)? Is there a built in function of JavaScript to convert a string into a particular locale (Euro in my case) E.g. The JavaScript language spec states that +x is equivalent to Number(x). Many developers use +x to convert a string to a number. You can also use a tool like archetype that handles some of these edge cases for you: archetype.to( '42', 'number') // 42 Number( '') // 0 Using Number(x) has several edge cases that may be correct depending on your perspective. But I think this is the source of the problem. Understanding NaN Alright, let's move on to understanding what NaN is. typeof parseFloat( '42') // 'number' Number.isNaN( Number( '42')) // false typeof parseFloat( 'fail') // 'number' Number.isNaN( Number( 'fail')) // true Summary Just to be super clear, the difference between these 2 methods is that Number.isNaN doesn't coerce or forcefully convert the argument to a Number before determining whether it has the value NaN. You should not use the global isNaN() function. Various methods provided by Javascript can be used to convert the string into a number only if the string characters are convertible into numbers, otherwise. For strings, Number () returns a number or NaN. For dates, Number () returns milliseconds since Janu00:00:00. Notes For booleans, Number () returns 0 or 1. ![]() If the value cannot be converted, NaN is returned. You should always use Number.isNaN() to check if the conversion failed. Description The Number () method converts a value to a number. The TLDR is you should use to convert generic JavaScript values to numbers if you want to be permissive, or parseFloat(x) if you want to be more strict. I'll also describe how to enforce these rules with eslint. In this article, I'll cover the tradeoffs of parseFloat() vs Number() and Number.isNaN() vs isNaN(). With NaN, implicit radixes, and numbers vs Numbers, there are a lot of ways to shoot yourself in the foot. Converting a string to a number in JavaScript is surprisingly subtle. ![]()
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