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JavaScript JavaScript Numbers Working with Numbers Convert Strings to Numbers

Victor Stanciu
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Victor Stanciu
Full Stack JavaScript Techdegree Student 11,196 Points
Posted by Victor Stanciu
.a{fill-rule:evenodd;}techdegree
Victor Stanciu
Full Stack JavaScript Techdegree Student 11,196 Points

Why is "typeof +pi" number, but "typeof(+pi).toFixed(2)" is string?

Hi!

I tried eliminating the possibility of a false return in case the user inserts, for example, 3.14159. For this, I converted the string pi to number using +pi, and then kept only the first two decimals, using (+pi).toFixed(2).

The problem appears when comparing (+pi).toFixed(2) === 3.14. Apparently (+pi).toFixed(2) is a string, and not a number. Why is that? My code is posted below.

const pi = prompt("What is pi?");
// this shows clearly the variable types.
console.log(typeof pi, typeof +pi, (+pi).toFixed(2), typeof (+pi).toFixed(2));
console.log((+pi).toFixed(2) === 3.14);

Thanks so much for your help!

1 Answer

Steven Parker
Steven Parker
231,248 Points
Steven Parker
Steven Parker
231,248 Points

As you discovered, toFixed() returns a string by design, since it is generally used in formatting output.

There are four easy ways around this to accommodate what you're doing:

console.log((+pi).toFixed(2) == 3.14);          // use a coercable ("normal") comparison
console.log(+(+pi).toFixed(2) === 3.14);        // convert the result back into a number
console.log((+pi).toFixed(2) === "3.14");       // compare with a string
console.log(Math.round(+pi*100)/100 === 3.14);  // use an entirely numeric alternative