Get the Difference Between Two Arrays in JavaScript

Sometimes we want to compare the difference between two arrays in JavaScript and return the remaining values in a new array.

This can be useful for inventory or purchase management where we could compare the selected items against the available stock, for example.

In this tutorial, we will cover two approaches to this:

  1. A single set of unique items in an array.
  2. A main array containing duplicate items.

Let’s get cracking!

Continue reading “Get the Difference Between Two Arrays in JavaScript”

Find the item with the highest order of importance and store it with JavaScript

I recently came across (yet another) situation where I needed to work with a text-based ranking system. You know, when some gem decided to create a ranking system like good, great, awesome, spectacular and then we need to store each user’s highest level of achievement over a period.

This occurs with surprising regularity in my work, most often when needing to work with spreadsheet data that a user has created. We can’t really change the data on the spreadsheet so we need to handle this with some code instead.

Not ideal, I know. We could complain about it ad nauseam or simply live with it and deal with it using some JavaScript magic.

In this tutorial, we will cover two approaches to this. Both approaches have their own uses. We will go over a few use cases so you get an idea of when these sorts of things come up.

Let’s get cracking.

Note: Sometimes it takes a couple of examples to figure out a concept. Other times, you can figure it out in an instant. Feel free to read as much as you need to understand the concept. 


Storing the most important text value with JavaScript

Example 1: Recording the best poker hand

Let’s say I am having a poker night with some friends and want to only record my best hand for the night, you know, to brag later.

First, we should list all the poker hands from best to worst:

  1. Royal flush
  2. Straight flush
  3. Four of a kind
  4. Full house
  5. Flush
  6. Straight
  7. Three of a kind
  8. Two pairs
  9. Pair
  10. High Card

As the night starts, my first hand was a ‘three of a kind’. So I make a note. Then, I only get a ‘pair’ for my next hand. I’m not writing that down. It’s worse. Next, I get a ‘flush’. Awesome, a ‘flush’ is better than a ‘three of a kind’, so I will store that one and put a line through my previous record.

Do you get the picture?

Cool. Let’s write some code.

We will need to store our list of poker hands in order and also create a variable to store the best hand we get during the game. We have two choices here. I will go through both and then discuss performance.

Storing data as an array

So what’s going on?

First, we store our list of all possible poker hands in an array called ‘poker’. Starting with the lowest hand on the left and finishing with the best hand on the right (bottom of the array). Lines 1-12

Arrays in JavaScript maintain their order so we know that “High Card” will always be in position poker[0] and “Royal Flush” will be in position poker[9]. We will be using the array’s order in a minute to check if we should be storing our next hand or not.

Next, we need a place to store our highest hand for the night. We set the variable bestHand for this, using JavaScript ‘let’ variable declaration to allow us to change the variable as we update it with a better hand. Line 14


We now create the function setMostImportant_Array(). This function takes 3 arguments:

  1. The array or list to reference
  2. The stored item, in our case, bestHand.
  3. The new contender item, which may or may not, be better than the stored one.

The function returns the most important item. This is done with a simple ternary operator, which is a kind of simplified ‘if’ statement.

On line 5, we compare the position of our stored bestHand value in its position in the poker array list against the new hand. We do this by using the indexOf method which returns the first occurrence of the matching item in an array as an index of that array. If the current bestHand is greater than or equal to the new hand then we return the current bestHand. Otherwise, we return the new hand.

Testing the results.

After we have set up our function we can now run it. Our second hand of the night was a ‘pair’ so we updated our best hand to our function adding in, poker as our array list, bestHand as our stored item, and “Pair” as our new item.

bestHand = setMostImportant_Array(poker, bestHand, "Pair");

Because a pair is not as important as a ‘three of a kind’ we kept the current value.

On the next hand, we got a ‘Flush’ which is more valuable than a ‘Three of a kind’ so using our function again we see that bestHand now stores the ‘Flush’ as the most important value.

Storing Data as an object

We can achieve the same outcome by storing data as an object. Let’s take a look at the code.

In our poker object, we store the names of each hand as a property string and then each property’s value is its position or order of importance in the group of data. Lines 1-12

Our setMostImportant_Object() function is a lot simpler than the array function above. Here we will use our ternary operator, but this time we simply are checking to see if the bestHand property value stored in our poker object is greater than the new hand property value. Line 14-24

Our function takes on arguments in the same way as the array function and will store the new property in the bestHand variable if the hand is better than the one stored.

Which is better? The array or object approach?

The most predictable and irritating answer first. It depends.

Running a benchmark test on the two they are fairly comparable, but over larger sets of stored ranked text, the object approach would perform better.

However, my preference would slant to the array approach if my ranking is not static. This is probably a rare case, but imagine if your text-based ranking system changes regularly and you need to update the order of you ranking system.

Moving your data around an array and cutting it out of one position and putting it in another is fairly simple with an array. With an object, however, we need to update the current value of the property that is going to change and then move all the other properties around than need to change. This would definitely be more memory intensive and harder to code.

Here is an example.

Example 2: Getting the best commodity in a fluctuating market

Imagine that we are investing in a fictional commodity market. As supply and demand fluctuate, a commodities value may move to become greater or lesser than other commodities in the same market.

Our goal in this scenario is to keep the best value commodity available to us. If the commodity’s value position compared to other commodities shifts, then we need to ensure that we always keep the best commodity available to us.

Let’s use this fictional list of commodities as our example:

  1. tryzatium << currently lowest value.
  2. ocoumbre
  3. malcatite
  4. enzome
  5. parl
  6. obvoster << currently highest value

We are first presented with the opportunity to buy ocoumbre. Having no investments in the market, we make the purchase.

Our next opportunity is to purchase tryzatium. Currently, this item is less valuable than ocoumbre so we won’t buy it.

Enzome comes up next. Being of higher value, we purchase it and sell off our ocoumbre. 

Then the next day the market changes.  A new large deposit of enzome is found and floods the market, reducing its value to below tryzatium. So when we get an offer to buy malacite we jump at it.

Let’s write some simple code to simulate this.

storing data in a fluctuating ranking system

The results of which should appear like this:

Just like in the first example, when a better commodity is presented to us we replace it with our current commodity. When there is a change to the order of the market, then we also see a change in how we prioritise what we keep.


The moveItem() function allows us to change the order of priority of our list of commodities.

The function takes 3 arguments as parameters:

  1. list – the array of ordered items. In the example, this is our commoditiyByVal array.
  2. item – This is the item in the list that needs to change position.
  3. newIdx – The new index or place in the list that the item needs to move to.

In the first task of the function, we need to get the current index of the item. We do this by finding its index in the array with the indexOf method. Line 8

Next, we use the JavaScript splice method to cut the item out of the array (The inner splice) and then add it back into the array at the desired location (The outer splice). Line 9

The outer splice takes 3 arguments:

splice(start index, deleteCount, item to add)

  1. start index – our new index for the position of the item.
  2. delete count – the number of items to delete. For us, this is zero. We only want to add an item.
  3. item to add – This will be the item that we splice out. Not only does splice update an existing array, but it can also return the items that have been removed as an array. This is handy for us because we will use them in this last argument. This inner splice takes two arguments:
    1. start index – the current index of our selected item.
    2. delete count – one, the current item we need to move from the existing position.

Why I recently needed to store the most important item in a list in JavaScript?

Example 3: Time Trigger (Cron Job) efficiency

So the thing that actually compelled me to write about this was a part of a Google Apps Script project – Google Apps Script is built on Google’s V8 engine for EcmaScript  JavaScript.

I was fetching requests from an external API that requested that an event be triggered at a particular interval. We use Clock Triggers in Google Apps Script but you might know them as Cron Jobs.

The API contained a list of text-based triggers that looked a little like this:

  1. “daily”,
  2. “6 hours”,
  3. “1 hour”,
  4. “30 minutes”,
  5. “1 minute”

Anyway, we have limitations and quotas to how many clock triggers we have running in one account at one time so I always try and limit these. So if I can set a daily trigger for a user I will prefer it over a 1-minute trigger so that they don’t get any quota errors or issues.

In my example, when a user requires a trigger to be set for a project at a certain interval, the code will check against the current setting of all existing triggers for the project and update the trigger accordingly.

So for example, if a user sets their first project item to run every six hours, then the trigger will only run every six hours. If they add another item that needs to be run daily then that item will be initiated every fourth time the trigger is run ( 4 x 6 = 24 hours).

However, if they create a third item that requires it to be run every 30 minutes then we need the change the frequency that the trigger is called to 30-minute intervals. This means that the first item needs to be invoked every 12th occasion the 30-minute trigger is run (6 x 2 = 12). Likewise, the daily trigger needs to be invoked every 48th time the trigger is run (24 hrs x 2).

Let’s see how this looks in the code:

The code


I’d love to hear if you have some examples of when you might need to handle text-based ordering systems and what approach you took. Feel free to add them in the comments below.

If you have found the tutorial helpful, why not shout me a coffee ☕? I'd really appreciate it.

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Get a Unique List of Objects in an Array of Object in JavaScript

Recently, I needed a way to ensure that my JavaScript array of objects does not contain any duplicate objects based on an ‘id’ key. While I do enjoy more common approaches to this solution with the use of a simple ‘for’ loop it is always a bit of fun to see how folks have come up with modern solutions.

It wasn’t too long before I stumbled across this ES6 one-liner:

Pretty neat, huh?

Here are two locations I found them:

But as many code oneliners are, they are a little tricky to understand. So I wanted to spend some time understanding how this worked and thought, you might find this a little interesting too.

Let’s take a look at an example and then work through each bit as we go.


The Example

In the example above, we want to create a unique array of objects based on the ‘name’ property of each object set.

You can see that there is a duplicate property in positions 1 and 4 with key ‘name’ and value, ‘Alessia Medina’ that we need to remove.

You can also change the key to either the ‘character’ or ‘episodes’ property.

When the distinct array of objects is created it will set the last duplicate object as the object value. Why? Because the script will essentially reassign the ‘name’ property each time it loops through the array when creating the new map.

Let’s start breaking down the script so we can see how each one operates.

Code Breakdown

The first task of this script remaps the array of objects using the JavaScript map() method. This method takes a function, which in our is an arrow function.

Map method arrow functions generally look like this:

As an ordinary function, it would look like this:

In our example above, we have our callback arguments on a new line so we will also need to include curly braces {}.

With the map method, the function will act on each array and return the result to generate a new array of the same length.

For us, our call back condition rebuilds each array to make a sub-array containing the value of each name key in the array as the zeroeth element and the object at the first element.

So the first element in the new array will look like this:

new Map

A quick side example

Before we continue, let’s take a quick look at a basic Map process on a 2d array:

To be frank, I didn’t really understand the Map object too well until I explored this script.

Map object stores key-value pairs similar to an Object. However, the Map maintains the insertion order of the properties. You’ll see Map objects often displayed like this when logged out in the console.

Map can be iterated through in a similar way to a 2d array with the zeroeth element as a key and the next element as a value for each property of the map – ['key', 'value'].

Alternatively, we can also generate a Map from a 2d array as we did in the example above – turning each sub-array into a key-value pair.

Back to our main example…

new Map of our example

We are using the data we retrieved from our previous example here to remove some of the clutter from the process. I have added those results at the top of the code block above.

In this example, we simply apply new Map to this array of data. By doing this Map turns into a type of Object with a key-value pair. Now keep in mind that Object keys are the highlander of data types – there can be only one.

What does this mean beyond a bad joke that really shows my age?

It means that each key must be unique. All of our keys are now the names of our users. The new Map constructor process will then iterate through each name and store it and then assign its value. If a key already exists it will overwrite it with this next value with the same key name.

This means that the last duplicate key will always be displayed. Effectively only storing unique values.

Displaying the keys of each property in the Map

We can generate iterators to go through each key or value with the keys() and values() methods respectively.

We will have a look at the keys() method first quickly.

Let’s apply keys() to our test_uniqueObjArray_NewMap Map we generated above.

As you can see this produces an iterator of all the (unique) keys in our data as a Map Iterator. It’s not quite an array of objects, but it allows us to iterate over each key to do something with it.

The same is true for the values() method.

Displaying the values of each property in the Map

Here we want to get an iterator of our values so that we can recreate an array of objects again.

Using the values() iterator method we now have our Map values ready to go.

Using the spread syntax to create our array of object

Now that we have an iterator of our unique values we can now place them in our spread syntax – “...“.

When you apply the spread syntax on an array, it will add each item of an iterable to the array. Take a look at what it does to our Map values.

This is similar to using the Array.from() static method that would look like this:


So how does this one-liner stack up against a more traditional for-loop like this?

Surprisingly better than I thought it would, to be honest.

Running a benchmark test with, the one-liner ran only 13.74% slower. Which is pretty good compared to some of the other options I found out there.


So should you be using this oneliner over the for loop? Is an impressive one-liner better than something more clear? To be honest, I am on the fence.

I do like the way this script operates. It is clean and once I got my head around the Map object, it did make a lot of sense. I think if I saw something like this in the wild I could pretty easily identify what it was for and see that it was a nice short solution to a problem.

I don’t think I would use this approach when I need to iterate over objects in the many thousands. Then speed becomes important. But if I need something in my toolkit to solve a problem like this, then I am definitely going to use it.

I have an example of how I used the code to check for duplicate selections of files in Google Drive here:


What do you think? Is it too abstract or is it elegant?

Did this tutorial help you understand the JavaScript one-liner better? Do you think you would apply it in your own projects?

Please let me know your thoughts in the comments below. I really enjoy hearing how things are used in the wild.


Create Removable Item Buttons Generated From Select or Comma-separated Input elements with HTML, CSS and JS

I am currently working on a larger project at the moment that requires a lot of front-end wrangling. As a part of this project, I needed to create Button Items that are generated by the user from both an HTML select element for one section and, a comma-separated text input in another section.

When a user selects an item from a select menu, a button appears in a desired area with the name of the selection and a small “X” that can be clicked to remove the item. Likewise, if a user wishes to create a bunch of items separated by commas in an input element and either hit the “Enter” or the “Add” button, then those items will be transformed as a bunch of individual buttons that the user can remove and change.

The buttons essentially become the user’s selection of items.

I also needed to be able to get a list of those item buttons for when I submit a form server-side or for some other task.

As a result, I created a small library called itemButton().

Note: If you have a bit of experience with front-end, then all you may need is to grab the CSS code and input.js file. If you need some further explanation you can find the information below.

What it does

The itemButton() library:

  1. Creates a button named by the selection or the user’s input, This is removable should the user wish to change their choices.
  2. Allows you to select the max number of items you want your users to be able to choose.
  3. Easily extracts a list of buttons by ID and value.

An example

Take a look at an example:

My inability to consistently fail to place an ‘e’ at the end of giraffe notwithstanding, you can see that the user can select items from a select element and they will be displayed in a chosen area below. Further, when the user types some words and separates them by a comma they are displayed as buttons in a div below it.

Limit the number of displayed Item Buttons

You might have also noted that the select element will only display two-item buttons, while the comma-separated list will display up to 10. You are able to create a maximum limit of any of your text input or select elements you are running itemButton() on.


When the user submits their items, itemButton() will:

  • Check for duplicates. If it already exists, it won’t be displayed again.
  • Remove any empty comma-separated elements.
  • Remove any non-alphanumeric characters.
  • Cut any text input items between commas to less than or equal to 25 characters (You can change this if you want).
  • Exchange any spaces between words with a dash for the button ID.
  • Any item starting with a number gets and “a” at the start of the button ID so it can be used in the HTML.

Getting a list if item buttons

As you can see in the video above, when the user clicks the Log Items button, an object of ids and values for each item is listed in the browser console using the list() method in itemButton(). This is most useful for when you are submitting data to the server.

Let’s have a gander at the code:

The Code

I have chosen to put the Javascript itemButton() library in an input.js file. In my project,  I have other small classes or libraries in that file too. It is up to you how you want to add the code.

The CSS for the buttons is separate, and I have added it to my universal style.css file. Again you can put it anywhere you think works for you.



Add this to your main CSS file.

Quick use guide

Create the select button or input button

First, you will need to create your select or text input elements. Make sure that they have an appropriate ID that we can reference later.  You can have as many select or text input elements as you want to reference the itemButton() class.

Take a look at the example below:

Here we have added a select element with an id of “items”. We also have a text input with an ID of “tags”. The “tags” element also has an “addTag” button that the user can use to add their tags.

Create a div or span for your item buttons to go

Next, we need to create a location to display your item buttons. In the example below, I have used a div directly below the select or input elements.

Importing the itemButton() code

Our next step will be inside the script tags of our HTML file. If you are importing just the input.js file into your HTML file you will need to invoke you script tags as a module :

If you are importing more than one file, like I am in the example, I recommend you import your Javascript files like this:

In the example above, my two files are in the resources folder. The items.js file is just the file I have stored my list of select items.

Add event  listeners

Your next task is to add event listeners for each of your elements. For me, I will add an “input” event for my select element.

For my text input, I will add both a “keypress” (Enter) listener if the user hits enter after typing in their items in the “tags” text input or a “click” if they hit the “Add” button. We will also clear out the tags after each use.

Take a look at the example:



Now it’s time to add the button. We do this inside each event listener.

The add() method takes three arguments:

  • items – A string containing a single item or comma-separated list of items.
  • selectionsLoc – This is a string containing the ID reference of the location you want to display your buttons, usually in a div or span.
  • >numSelections – The maximum total number of items you wish to have the user select.

itemButton().add(items, selectionsLoc, numSelections)

Back to our example for our select element, our item is the value of the current selection. The location that we want to display our item buttons is theitems-selection div and the maximum number of items that our user can add is 2.

For our text input, the value is the comma-separated string of values that the user enters. The location the button items will be displayed in will be the tags-selection div and we will allow the user to add up to 10 items.


To get a list of item buttons from any of your assigned areas that display them, you can use the list() method.

This method takes one argument, the element id that the item buttons are contained in. The list method will return an object of key-value pairs containing:

The example

This example file setup is as follow:

  • index.html
  • main.css
  • resources
    • inputs.js
    • items.js

Here is the sample HTML file below:

And the resources > items.js file for the select element.

The Wrap Up

I hope you found this small library useful for creating your own buttons. You may wish to make style changes to your buttons to match your own colour theme.

You may also wish to extend or reduce the length of characters for each item. You can do this in the input.js file on line 37.

You can download a copy of the example here:

I really like hearing how people apply these components to their own projects. Feel free to share in the comments below.

If you found this tool useful, please click the like button so I know that I am making good content. Or if you want to get updates on my latest posts, please subscribe (below the comments).



Google Apps Script – Javascript: Emulate the “Proper” Google Sheets Function

Google Apps Script / Javascript

I just had a recent email from a reader who asked how to tidy up a user’s inputted name from say, a Google Form so that all the first letters of each work in the name are capitalised in the same way that the Google Sheets Proper function does.

I thought it would be a good idea to provide a quick reference for the reader and myself for future projects.

The Code

Continue reading “Google Apps Script – Javascript: Emulate the “Proper” Google Sheets Function”