Repository navigation
About isNaN #148
Description
In the "Conditional execution" section of Chapter 2:
var theNumber = prompt("Pick a number", "");
if (!isNaN(theNumber))
alert("Your number is the square root of " +
theNumber * theNumber);With this modification, if you enter “cheese”, no output will be shown.
The string "cheese" is surely "not a number". But "not a number" has a specific meaning for numbers represented as IEEE-754 floating-point values. This is confusing.
I suggest replacing the isNaN function with the typeof operator (typeof "cheese" !== 'number'). Or at least use the Number.isNaN() function in ES6:
isNaN("cheese") //true
Number.isNaN("cheese") //false
Activity
Restore explicit Number conversion in square root example
marijnh commentedon Dec 14, 2014
I am not trying to use
isNaNas atypeofequivalent here (after all,promptwill never return a number). Rather, I'm testing whether the string holds a valid number. For some reason, the explicitNumberconversion that I used to have here got dropped in an apparently unrelated patch (d7c72a4). Not sure what I was doing there, but attached patch restores it.