Wouldn't it be nice to assign the result to variables like firstName and lastNa… There is some ambiguity to clear up here - cat: dog. Maps have elements of both Objects (a unique key/value pair collection) and Arrays (an ordered collection), but are more similar to Objects conceptually. The obvious problems like trying to destructure a map with the list syntax could obviously be caught by analysis, but the specific form could not necessarily be statically analyzable. var func = => {foo: 1}; // Calling func() returns undefined! Given this array of Nigerian states: Using Array de-structure, you would get the first, second and the fourth elements from the statesarray, thus: This is a huge (pronounce as you-dge for me, pls) improvement from pre-Array de-structuring days where we would have to access these three elements individually and usually on separ… You can then destructure them directly into a new object. Though hard to conceive, the process is actually very simple in practise. Learn how to get the last element from the array in javascript. It’s not the only way, of course, there’s also for .. in and other approaches, though this is my preference. We can take it a step further by assigning a new variable to the value like so. This uses destructuring and arrow functions to greatly simplify our code. Let’s bring back the first code snippet we saw when we embarked on this journey. Object destructuring was one of those. There might be a situation where you want to collate a certain number of items in an array while you extract others. displayFunction({ details: {userName}, messages }), displayFunction({ details, messageTransactionLog: messages }), displayFunction({ details: {displayName: userName}, messageLog: messages }), displayFunction({ details: {displayName: userName = "Anon"}, messageLog: messages = [] }), var adultUsers = users.filter(function(user){. Instead of accessing elements in an Array with their index number, ES6allows you to assign the array to another array that contains variables in the same index as the element you need. So we can omit it entirely and destructure right in the function definition. It can be clear from the following example. Knowing how they work and what they do can make it much easier to write better React, and much easier to read it. Array access isn’t as reliable as objects, so you can firm things up by skipping elements [firstName, lastName, , emailAddress] or by providing default values using the syntax [firstName, lastName, status="Active"]. This will give us only userName and messages. From what we have covered so far, you can see that the variable maps to the value that matches its position. Destructuring assignment is a special syntax that allows us to “unpack” arrays or objects into a bunch of variables, as sometimes that’s more convenient. Even though the phone variable was not created initially, we now have a value for it that we can go on to make use of. The destructuring assignment allows you to assign items of arrays or properties of objects to separate variables. Here is an example that computes the name of the object property by using "Computed Property Name" notation: Javascript map array of objects. The destructuring assignment uses similar syntax, but on the left-hand side of the assignment to define what values to unpack from the sourced variable. Think about it for a moment. These variables will have the values they were paired with when the object was created. In this syntax: The identifier before the colon (:) is the property of the objec… It will be undefined. That’s no magic, let’s step back a little, and a little more. If payload or q… 4 – Because this is an array, we need to map() over it, to retrieve the data from every row. If you cannot come up with an answer let’s see that in practice. If you would like to see destructuring in action, take a look at How To Customize React Components with Props, which uses this syntax to destructure data and pass it to custom front-end components. Specifically, notice in the function arguments the expressions = {} which in JavaScript will set a default value of {} for the parameter if it is undefined. It means that to extract the first and second values, we only need two variables, like so. This might be tricky, here’s a good hack you can make use of if you know the length of the array, the number of commas you should have must be equal to the number of items you want to skip plus one. There are no rules on the number of items that can be skipped, other than using commas in place of the item(s) to be skipped. The syntax here is relatively ambiguous, cat is going to have a different value based on the structure. The rest operator will collect the rest remaining data (the key and value pair) in an object. If you can always remember the differences between array and object destructuring, it will be easy to work with mixed destructuring. var func = => {foo: function {}}; // SyntaxError: function statement requires a name. What happens when we want the first, second, and last values. This capability is similar to features present in languages such as Perl and Python. # JavaScript Array.flatMap() You learned how Array.flat() flattens an array in my previous tidbit. The function getUserNameById() returns the first name, the middle name, and the last name for a user at a given userId. That’s very possible, we’ll have to make use of a comma in the place of the values we want to skip – instead of having a variable in that place, we’ll use a comma. This might be the values that come in from some sort of data access tool. When destructuring the inner object, we had to specifically add the key of the object, without that we will not be able to extract the values contained in it. 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