First, let's review how you transform lists in JavaScript. Given the code below, we use the map() function to take an array of numbers and double their values.
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But the main difference is that the Map allows keys of any type. A Map object iterates its items in insertion order and using the for…of loop, and it returns an array of [key, value] for each iteration. The JavaScript map object is a type of collection that allows storing values based on key-value pair terminology. The map object is introduced in the ES6 specification of JavaScript and it allows storing the pairs of keys and respective values in it. This kind of data structure is useful when we need to store the values as pairs. Introduced in ECMAScript 2015, Maps in JavaScript are ordered collections of key/value pairs, and Sets are collections of unique values.
It returns if the element is … map.set (key, value) – stores the value by the key. map.get (key) – returns the value by the key, undefined if key doesn’t exist in map. map.has (key) – returns true if the key exists, false otherwise. map.delete (key) – removes the value by the key.
Ther e are two main differences between Maps and regular JavaScript objects. 1. Unrestricted Keys. Each key in an ordinary JavaScript object must be either a String or a Symbol.
Rose Gold Penny Round Stainless Steel Mosaic Factory Kina · Nike Air Penny II Varsity Royal 333886 005 · www.escapade · Nike Air Max Penny · Penny Stocks. Map 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.
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So here’s a breakdown of what it does exactly, and how to use it. And by the way, if you need to catch up on JavaScript itself, I suggest you check out our JavaScript Primer first.
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