Category: Javascript

Is a Year a Leap Year? Gregorian Calendar & JavaScript

Earth doesn’t perfectly orbit the Sun every 365 days. Rather, it irritatingly must make its orbit in oh, I don’t know, roughly 365.242190 days each year.

Due to this inconsiderate behaviour, we must add a leap year into our common calendar known as the Gregorian Calendar.

Like, I presume, many of us, I thought a leap year occurred every four years.

Whether it was a matter of being taught a half-truth from my school teachers many decades ago in School (possible), or simply not paying attention to said teachers (much much more possible), I was wrong on this account.

So, when is a leap year?

According to the very impressively sounding Royal Museum Greenwich, a leaps year must meet the following conditions:

  1. Any year that is a century (e.g. 2000, 2100, 2400, 1900) must be divisible by 400. So 2000 and, 2400 are leap years but 2100 and, 1900 are not.
  2. Any other year must be divisible by 4.

Yeap. It’s that first one, I didn’t know about.

So with this in mind, how would we determine if a year is a leap year in JavaScript?

Enter the JavaScript Modulo Operator

To determine if something is divisible by a number we can use the JavaScript modulo operator (%) to determine the remainder. If the remainder is zero we know it is divisible by a number.

So 12%4 would return 0 because 12 divides perfectly into three lots of four. Whereas 7%3 would have one left over.

Got it? Cool.

The Video

The Video Tutorial

Releases  17 Sep 2024

The Code

Let’s now create a function called isLeapYear() that takes a four-digit number for our target year.

Remember our leap years rules.

We need to:

  1. Check if the year is divisible by 400 (year%400 == 0)
  2. Check if the year is divisible by 4 (year%4 == 0)
    If it is, then:
  3. Check if the year isn’t divisible by 100 (year%100 != 0).

Give it a run to see the results.

Why not just use the Date object?

I actually did this in a previous tutorial to get a list of days of the year a particular weekday (e.g. Monday, Tuesday, Wednesday…etc) falls. You can check it out here:

Get the Day of the Year in JavaScript

However, I would say that a purely numerical approach is always going to significantly beat a multi-step constructor approach.

Check out this benchmark example:

benchmark JavaScript find leap year numerical approach vs Date construtor approachBig difference.

 

~Yagi

Get the Day of the Year in JavaScript

Sometimes it can be handy to find the day of the year* that a particular date falls on in JavaScript.

Let’s say you want to get the day of the year for Pie Day (14 Mar 2024). Check out the code:

*This tutorial is for the Gregorian Calendar.

Continue reading “Get the Day of the Year in JavaScript”

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

setMostImportant_Array()

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.

moveItem()

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

Conclusion

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.

Create and Publish a Google Workspace Add-on with Apps Script Course

Need help with Google Workspace development?

Go something to solve bigger than Chat GPT?

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Schedule a free consultation today to discuss your needs and get started or learn more about our services here.

 

~Yagi

 

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

myObjArray.map

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.

Rucoy Highlander GIF from Rucoy GIFs

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:

Performance

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 jsbench.me, the one-liner ran only 13.74% slower. Which is pretty good compared to some of the other options I found out there.

Conclusion

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:

https://yagisanatode.com/2021/06/27/creates-a-google-workspace-add-on-file-picker-card-with-cardservice-that-opens-a-google-picker-in-an-overlay-window-google-apps-script/

 

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.