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JavaScript JavaScript Array Iteration Methods Array Manipulation Transform Array Items with map()

Posted by Ewerton Luna
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Ewerton Luna
Full Stack JavaScript Techdegree Graduate 24,031 Points

I don't understand why I'm able to use .toFixed on an integer

Looking at this snippet:

const prices = [5, 4.23, 6.4, 8.09, 3.20];
const formattedPrices = prices.map(price => `$${price.toFixed(2)}`);

I thought that .toFixed() couldn't be used on the integer value directly, since it is a primitive value. In my mind, it had to be either be used like this:

const prices = [5, 4.23, 6.4, 8.09, 3.20];
const formattedPrices = prices.map(price => `$${Number(price).toFixed(2)}`);

Or creating an instance of Number like this:

const prices = [5, 4.23, 6.4, 8.09, 3.20];
const formattedPrices = prices.map(price => {
    priceNumber = new Number(price);
    return `$${priceNumber.toFixed(2)}`}
);

Could someone help me understand why and how the first snippet works? Thank you!

1 Answer

Clayton Perszyk
MOD
Clayton Perszyk
Treehouse Moderator 48,850 Points
Clayton Perszyk
Clayton Perszyk
Treehouse Moderator 48,850 Points

A simple explanation:

JavaScript will coerce primitives into objects to access properties and methods. The object is discarded and garbage collected after it does its job.

https://javascriptweblog.wordpress.com/2010/09/27/the-secret-life-of-javascript-primitives/