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The Map object in JavaScript is a collection of key-value pairs where both keys and values can be of any type, including objects, functions, and primitives. Unlike objects, Maps maintain the order of their elements based on the insertion sequence, making them more predictable for iteration.
Key Features of Map
Unique Keys: Each key in a Map is unique. If you set a key that already exists, the value will be updated.
Insertion Order: Maps maintain the order of elements based on their insertion sequence.
Any Data Type: Keys and values in a Map can be of any data type, including objects, functions, and primitives.
Size Property: The size property returns the number of key-value pairs in the Map.
Basic Operations
Creating a Map
To create a new Map, you can use the Map constructor:
const myMap = new Map();Adding Elements
To add elements to a Map, use the set method:
myMap.set('key1', 'value1');myMap.set('key2', 'value2');Accessing Elements
To access elements, use the get method:
javascript - How can I check if two Map objects are equal ... - Stack ...
Mar 12, 2016 · Here's a one-liner function for checking map equality: const mapsAreEqual = (m1, m2) => m1.size === m2.size && Array.from(m1.keys()).every((key) => m1.get(key) === …
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Map - JavaScript | MDN - MDN Web Docs
- The Map object holds key-value pairs and remembers the original insertion order of the keys. Any value (both objects and primitive values) may be used as either a key or a value.
Equality comparisons and sameness - JavaScript | MDN - MDN …
Mar 6, 2025 · It's used by Array.prototype.includes(), TypedArray.prototype.includes(), as well as Map and Set methods for comparing key equality.
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Keyed collections - JavaScript | MDN - MDN Web Docs
Mar 6, 2025 · Both the key equality of Map objects and the value equality of Set objects are based on the SameValueZero algorithm: Equality works like the identity comparison operator === . -0 …
JS: Test Equality of Map Objects
Apr 20, 2024 · Test Map Equality /* xah_map_equal(xmapA, xmapB) return true if two maps have the same keys and values. Keys are compared by triple equal. Values are compared by triple …
JavaScript Map Reference - GeeksforGeeks
Dec 29, 2023 · JavaScript Map is a collection of elements where each element is stored as a key, value pair. Map objects can hold both objects and primitive values as either key or value. …
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Using Objects as Keys in JavaScript Maps: Short Notes on Key …
Apr 17, 2023 · Use objects as keys in JavaScript Maps by understanding how JavaScript compares objects by reference. By using a single object reference as the key, you can avoid …
JavaScript Maps - W3Schools
How to Create a Map. You can create a JavaScript Map by: Passing an Array to new Map() Create a Map and use Map.set()
Maps in JavaScript | Learn X By Example
JavaScript does not have a built-in maps package for utility functions. Instead, commonly used methods like size , clear , and others are already available on the Map object. For instance, to …
Map in JS - GeeksforGeeks
Feb 11, 2025 · Map () constructor allows two ways to create a Map in JavaScript. Passing an Array to new Map(). Create a Map and use Map.set(). set (key, val) : Adds or updates an …
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