JavaScript(JS) number method - tolocalestring

The toLocaleString() method is a built-in method of the Number object in JavaScript. It returns a string representation of the number formatted according to the locale settings of the user's system.

Here's an example usage:

const num = 123456.789;

console.log(num.toLocaleString()); // "123,456.789" in the US locale

In the above example, the toLocaleString() method is called on the num variable, which is assigned the value 123456.789. The method returns a string representation of the number formatted according to the user's locale settings. In the US locale, the decimal separator is a period and the thousands separator is a comma, so the output is "123,456.789".

The toLocaleString() method can also take optional arguments to customize the formatting of the output. For example:

const num = 123456.789;

console.log(num.toLocaleString("de-DE", { style: "currency", currency: "EUR" })); // "123.456,79 €" in the German locale

In this example, the method is called with two arguments. The first argument is a string specifying the desired locale ("de-DE" for German), and the second argument is an options object specifying that the output should be formatted as currency in euros. The output in the German locale is "123.456,79 €", where the decimal separator is a comma and the thousands separator is a period, and the currency symbol is the euro symbol.