I recently noticed thatisNaN('') andisNaN(null) both returnfalse in JavaScript. It means that both empty string andnull are valid numbers. So if you want to perform any number specific operation by just comparing the variable usingisNaN(), it won't work. Here is an example:

functionformattedAmount(x){if(isNaN(x)){return"Not a Number!";}return"$"+x.toFixed(2);}console.log(formattedAmount(""));// output: Error: x.toFixed is not a functionconsole.log(formattedAmount(null));// output: Error: Cannot read property 'toFixed' of null

This can be fixed usingNumber() function or+ operator. It will createNumber object of variablex. Hence both empty string andnull will result into number0 and accordingly, rest of the statement will be executed.

functionformattedAmount(x){if(isNaN(x)){return"Not a Number!";}return"$"+Number(x).toFixed(2);// OR// return '$ '+ (+x).toFixed(2);}console.log(formattedAmount(""));// output: "$ 0.00"console.log(formattedAmount(null));// output: "$ 0.00"console.log(formattedAmount(12.126));// output: "$ 12.13"

Hope you find it useful.

I made a quick check but didn't get why exactly in JavaScriptisNaN('') isfalse. I would love to know if you have anything to say regarding that. Thanks for reading!

Proofread by@ron4ex