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Nov 7, 2023 · Find various maps of the USA, including location, states, cities, capitals, national parks, rivers, lakes, and more. Learn about the history, geography, and culture of the USA with facts and images.
- Overview
- Description
- Static properties
- Static methods
- Instance properties
- Instance methods
- Examples
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.
Map objects are collections of key-value pairs. A key in the Map may only occur once; it is unique in the Map's collection. A Map object is iterated by key-value pairs — a for...of loop returns a 2-member array of [key, value] for each iteration. Iteration happens in insertion order, which corresponds to the order in which each key-value pair was first inserted into the map by the set() method (that is, there wasn't a key with the same value already in the map when set() was called).
The specification requires maps to be implemented "that, on average, provide access times that are sublinear on the number of elements in the collection". Therefore, it could be represented internally as a hash table (with O(1) lookup), a search tree (with O(log(N)) lookup), or any other data structure, as long as the complexity is better than O(N).
Map[@@species]\t
The constructor function that is used to create derived objects.
Map.groupBy()\t
Groups the elements of a given iterable using the values returned by a provided callback function. The final returned Map uses the unique values from the test function as keys, which can be used to get the array of elements in each group.
These properties are defined on Map.prototype and shared by all Map instances.
Map.prototype.constructor\t
The constructor function that created the instance object. For Map instances, the initial value is the Map constructor.
Map.prototype.size\t
Returns the number of key/value pairs in the Map object.
Map.prototype[@@toStringTag]\t
Map.prototype.clear()\t
Removes all key-value pairs from the Map object.
Map.prototype.delete()\t
Returns true if an element in the Map object existed and has been removed, or false if the element does not exist. map.has(key) will return false afterwards.
Map.prototype.entries()\t
Returns a new Iterator object that contains a two-member array of [key, value] for each element in the Map object in insertion order.
Using the Map object Using NaN as Map keys
NaN can also be used as a key. Even though every NaN is not equal to itself (NaN !== NaN is true), the following example works because NaNs are indistinguishable from each other:
Iterating Map with for...of
Maps can be iterated using a for...of loop:
Iterating Map with forEach()
Maps can be iterated using the forEach() method:
Code sample
var myMap = new Map();var keyString = "a string",keyObj = {},keyFunc = function () {};myMap.set(keyString, "value associated with 'a string'");...Find local businesses, view maps and get driving directions in Google Maps.
Nov 27, 2023 · The map() method of Array instances creates a new array populated with the results of calling a provided function on every element in the calling array. Try it. Syntax. js. map(callbackFn) map(callbackFn, thisArg) Parameters. callbackFn. A function to execute for each element in the array.
2 days ago · Learn about the art and science of making maps and charts of the Earth and other celestial bodies. Explore the history of cartography from ancient times to modern methods and applications.
set. collection. is. robust. Is this value a JS Map? This module works cross-realm/iframe, and despite ES6 @@toStringTag.. Latest version: 2.0.3, last published: 21 days ago. Start using is-map in your project by running `npm i is-map`. There are 518 other projects in the npm registry using is-map.
Feb 20, 2024 · A map is a symbolic representation of selected characteristics of a place, usually drawn on a flat surface. Learn about the common features of maps, such as scale, symbols, grids, and projections, and how they show information about the world.
