None. However, all objects that override this method are expected to accept at most two parameters, corresponding to locales and options, such as Date.prototype.toLocaleString. The parameter positions should not be used for any other purpose.

The return value of calling this.toString().

All objects that inherit from Object.prototype (that is, all except null-prototype objects) inherit the toLocaleString() method. Object's toLocaleString returns the result of calling this.toString().

This function is provided to give objects a generic toLocaleString method, even though not all may use it. In the core language, these built-in objects override toLocaleString to provide locale-specific formatting:

• Array: Array.prototype.toLocaleString()
• Number: Number.prototype.toLocaleString()
• Date: Date.prototype.toLocaleString()
• TypedArray: TypedArray.prototype.toLocaleString()
• BigInt: BigInt.prototype.toLocaleString()

The base toLocaleString() method simply calls toString().

const obj = {
  toString() {
    return "My Object";
  },
};
console.log(obj.toLocaleString()); // "My Object"

Array.prototype.toLocaleString() is used to print array values as a string by invoking each element's toLocaleString() method and joining the results with a locale-specific separator. For example:

const testArray = [4, 7, 10];

const euroPrices = testArray.toLocaleString("fr", {
  style: "currency",
  currency: "EUR",
});
// "4,00 €,7,00 €,10,00 €"

Date.prototype.toLocaleString() is used to print out date displays more suitable for specific locales. For example:

const testDate = new Date();
// "Fri May 29 2020 18:04:24 GMT+0100 (British Summer Time)"

const deDate = testDate.toLocaleString("de");
// "29.5.2020, 18:04:24"

const frDate = testDate.toLocaleString("fr");
// "29/05/2020, 18:04:24"

Number.prototype.toLocaleString() is used to print out number displays more suitable for specific locales, e.g. with the correct separators. For example:

const testNumber = 2901234564;
// "2901234564"

const deNumber = testNumber.toLocaleString("de");
// "2.901.234.564"

const frNumber = testNumber.toLocaleString("fr");
// "2 901 234 564"

• Object.prototype.toString()