Today I have learned map function and grid in javascript
Map function and Grid in javascript:
Description
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).
Key equality
Value equality is based on the SameValueZero algorithm. (It used to use SameValue, which treated 0 and -0 as different. Check browser compatibility.) This means NaN is considered the same as NaN (even though NaN !== NaN) and all other values are considered equal according to the semantics of the === operator.
Objects vs. Maps
Object is similar to Map—both let you set keys to values, retrieve those values, delete keys, and detect whether something is stored at a key. For this reason (and because there were no built-in alternatives), Object has been used as Map historically.
A grid is a collection of horizontal and vertical lines creating a pattern against which we can line up our design elements. They help us to create layouts in which our elements won't jump around or change width as we move from page to page, providing greater consistency on our websites.
A grid will typically have columns, rows, and then gaps between each row and column. The gaps are commonly referred to as gutters.
Defining a grid
Let's try out grid layouts with the help of an example. Download and open the starting point file in your text editor and browser (you can also see it live here). You will see an example with a container, which has some child items. By default, these items are displayed in a normal flow, causing them to appear one below the other. For the initial part of this lesson, we'll be using this file to see how its grid behaves.
Similar to how you define flexbox, you define a grid layout by setting the value of the display property to grid. As in the case of flexbox, the display: grid property transforms all the direct children of the container into grid items. Add the following CSS to your file:
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