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Intl Format Cache

A memoizer factory for Intl format constructors.

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This is a helper package used within Yahoo's FormatJS suite. It provides a factory for creating memoizers of Intl format constructors: Intl.NumberFormat, Intl.DateTimeFormat, IntlMessageFormat, and IntlRelativeFormat.

Creating instances of these Intl formats is an expensive operation, and the APIs are designed such that developers should re-use format instances instead of always creating new ones. This package is simply to make it easier to create a cache of format instances of a particular type to aid in their reuse.

Under the hood, this package creates a cache key based on the arguments passed to the memoized constructor (it will even order the keys of the options argument) it uses JSON.stringify() to create the string key. If the runtime does not have built-in or polyfilled support for JSON, new instances will be created each time the memoizer function is called.


This package works as an ES6 or Node.js module, in either case it has a single default export function; e.g.:

// In an ES6 module.
import memoizeFormatConstructor from 'intl-format-cache';
// In Node.
var memoizeFormatConstructor = require('intl-format-cache');

This default export is a factory function which can be passed an Intl format constructor and it will return a memoizer that will create or reuse an Intl format instance and return it.

var getNumberFormat = memoizeFormatConstructor(Intl.NumberFormat);
var nf1 = getNumberFormat('en');
var nf2 = getNumberFormat('en');
var nf3 = getNumberFormat('fr');
console.log(nf1 === nf2); // => true
console.log(nf1 === nf3); // => false
console.log(nf1.format(1000)); // => "1,000"
console.log(nf3.format(1000)); // => "1 000"


This software is free to use under the Yahoo! Inc. BSD license. See the LICENSE file for license text and copyright information.