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A simple Map which is almost identical to the es6 Map builtin. In fact it is a transparent facade over an internal Map builtin instance. To understand why this is useful see rationale.

Package includes Typescript libdefs. Suitable for node or browser environments. Supports native es imports in node > 13.2.


const Map = require('@iter-tools/map'); // OR
import Map from '@iter-tools/map';

Until Typescript supports package exports you must enable esModuleInterop to use this module.


@iter-tools/map adds two key pieces of functionality to the Map builtin:

First, the iter-tools Map class can be safely extended. While es6 permits the extending of builtin classes, such a practice tends to choke transpilers. This occurs because it is not legal for the Map builtin to be invoked as Map.call({}, entries), as it would be in transpiled code.

Second, the builtin Map has a shortcoming: it lacks a Map.isMap() comparable to Array.isArray. While it is possible to detect an instance with instanceof, that operator has shortcomings surrounding realms. For more reading on realms and instanceof, I recommend this Stack Overflow question.


The basic API is that of the Map builtin.

In addition the following is supported:

Map.isMap(inst): returns true if inst was constructed by this library and false otherwise. Note that it will return true even if the version of the library is different. It will return false for instances constructed with the Map builtin.

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  • conartist6