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Array behavior

From: Foundations of Programming: Fundamentals

Video: Array behavior

We are working with arrays and in JavaScript arrays are objects, and that's one of those words that sounds very generic, but it has a meaning in programming. We are going into what objects are but for now it just means they are more than dumb containers of data. Arrays are smart. They can tell us information about themselves. They have behavior. They can actually do things if we ask them to. And what do I mean by that? We have kind of seen some of this already. Let's say I create a variable that's just a string. But we have seen that we can use the .length property of that string variable to find information about the string.

Array behavior

We are working with arrays and in JavaScript arrays are objects, and that's one of those words that sounds very generic, but it has a meaning in programming. We are going into what objects are but for now it just means they are more than dumb containers of data. Arrays are smart. They can tell us information about themselves. They have behavior. They can actually do things if we ask them to. And what do I mean by that? We have kind of seen some of this already. Let's say I create a variable that's just a string. But we have seen that we can use the .length property of that string variable to find information about the string.

In this case, it would pop up the length of it being 24. I didn't have to go and count all the letters. The string itself actually knew what its length was, and we can use that same kind of format to find information about arrays. Let's say I use the shorthand format to create an array here with five elements ranging from position 0 through position 4. I could do something very similar that I did with the string and call myArray.length. In this case, it will pop up an alert box with the number 5. That's an important idea here.

It knows its length is 5. That is the length of the entire array, there are five elements in it, although bear in mind the highest index is 4. 0, 1, 2, 3, 4, but we are using the same .length property. It's smart enough to know that when we say .length on a string, it's how many characters are in the string. When we say .length on an array, it's what's the length of the array. Now we have already seen how we use functions in JavaScript. We use the name of the function with the opening and closing parentheses.

You can create them yourself. We can also use the built-in functions like alert. In this case, I am passing in information into that function. Or I can call a function, passing in information that also returns a value. So functions are used all over the place. But we also have the idea of methods and they are very, very similar, but a method is a function that belongs to an object. So instead of calling it directly, we actually use the name of the object, then a dot, then the name of the method.

And when I say some method here with the opening and closing parentheses, it's very much like calling a function. But we have to say what does this method apply to, what I am doing it on, and we have seen this before. If we have a string variable, we can use the .toUpperCase method to actually convert that to uppercase. And we have several very useful ones with arrays. So I can create multiple arrays and then call the different methods on each array. So let's say I use the shorthand format here. I am creating a new array and just putting some random stuff in it.

I have got an array with five elements. What I can then do is say myArray.reverse. I am using the opening and closing parentheses but I don't need to pass anything in. That will reverse all the elements of the array in place. 50 had been at position 4. It's now at position 0 and so on. We have other methods like .sort. That will sort them according to the rules of JavaScript sorting, if it's all alphabetical or numerical or a mixture of the two. We have .join. That will take all the elements of the array and combine them with commas and return them as a string.

We have useful little methods like .pop. If I call .pop on myArray it's going to take the last element, what's currently in there at oosition 4, and detach it and return that as a value. So we can pop something off the end of the array. Now the flip side of that, we also have .push. In this case I have to push a value on to the array and it will push it to the last element of the array. So these arrays are smart. They can tell us information, they have behavior. We can actually get to different pieces of them. And there is more that an array can do.

Now one of the questions you might have is when you're learning programming you might be thinking, "Am I supposed to remember all this?" Well no, at least not initially. You'll find that you will memorize the things that you've used but no programmer tries to memorize every single method on every single object. There are just too many. So the kind of thing that you do is you find a reference guide. Now with JavaScript I'm a big fan of the reference guide you can find at Mozilla.org. These are really the people that own JavaScript so it's a good example.

We jump into that Reference guide and what I will find is it breaks down all the different objects that are available, like array. I could go in and find some information about the array. it would give me a lot of descriptive stuff. But what I will find in the Table of Contents is there will be a section that says Properties, things like Length or Methods, and I could jump down to Methods and it would actually tell me, as I start to scroll down here, I have got the pop method which removes the last element from an array and returns that element. I have got the push method.

That will add one or more elements to the end of the array. I have got sort, I have got splice, and this is the way that you start navigating the language. You will find a reference guide for the language that you're working with and you start to explore the different pieces of the language as and when you need them. Don't try and memorize everything, because that's just not going to work. Just know where you can find the reference of the syntax. The ability to find what you need to in a reference guide is much more powerful than trying to memorize everything.

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This video is part of

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Foundations of Programming: Fundamentals

61 video lessons · 84633 viewers

Simon Allardice
Author

 
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  1. 4m 14s
    1. Welcome
      1m 16s
    2. Making the most of this course
      2m 8s
    3. Using the exercise files
      50s
  2. 22m 11s
    1. What is programming?
      5m 45s
    2. What is a programming language?
      4m 48s
    3. Writing source code
      5m 34s
    4. Compiled and interpreted languages
      6m 4s
  3. 16m 29s
    1. Why JavaScript?
      4m 45s
    2. Creating your first program in JavaScript
      6m 54s
    3. Requesting input
      4m 50s
  4. 31m 38s
    1. Introduction to variables and data types
      5m 16s
    2. Understanding strong, weak, and duck-typed languages
      3m 51s
    3. Working with numbers
      5m 4s
    4. Using characters and strings
      4m 5s
    5. Working with operators
      4m 47s
    6. Properly using white space
      6m 46s
    7. Adding comments to code for human understanding
      1m 49s
  5. 24m 49s
    1. Building with the if statement
      7m 35s
    2. Working with complex conditions
      4m 10s
    3. Setting comparison operators
      6m 59s
    4. Using the switch statement
      6m 5s
  6. 17m 56s
    1. Breaking your code apart
      4m 1s
    2. Creating and calling functions
      2m 57s
    3. Setting parameters and arguments
      6m 7s
    4. Understanding variable scope
      2m 23s
    5. Splitting code into different files
      2m 28s
  7. 13m 32s
    1. Introduction to iteration
      4m 28s
    2. Writing a while statement
      5m 24s
    3. Creating a for loop
      3m 40s
  8. 19m 28s
    1. Cleaning up with string concatenation
      4m 30s
    2. Finding patterns in strings
      8m 3s
    3. Introduction to regular expressions
      6m 55s
  9. 19m 59s
    1. Working with arrays
      5m 47s
    2. Array behavior
      5m 29s
    3. Iterating through collections
      5m 18s
    4. Collections in other languages
      3m 25s
  10. 10m 50s
    1. Programming style
      5m 55s
    2. Writing pseudocode
      4m 55s
  11. 25m 55s
    1. Input/output and persistence
      3m 6s
    2. Reading and writing from the DOM
      8m 11s
    3. Event driven programming
      7m 47s
    4. Introduction to file I/O
      6m 51s
  12. 24m 26s
    1. Introduction to debugging
      5m 57s
    2. Tracing through a section of code
      7m 5s
    3. Understanding error messages
      3m 21s
    4. Using debuggers
      8m 3s
  13. 14m 17s
    1. Introduction to object-oriented languages
      5m 18s
    2. Using classes and objects
      6m 29s
    3. Reviewing object-oriented languages
      2m 30s
  14. 11m 14s
    1. Memory management across languages
      5m 11s
    2. Introduction to algorithms
      4m 2s
    3. Introduction to multithreading
      2m 1s
  15. 29m 20s
    1. Introduction to languages
      1m 42s
    2. C-based languages
      4m 40s
    3. The Java world
      3m 13s
    4. .NET languages: C# and Visual Basic .NET
      6m 17s
    5. Ruby
      3m 4s
    6. Python
      2m 56s
    7. Objective-C
      4m 3s
    8. Libraries and frameworks
      3m 25s
  16. 1m 2s
    1. Where to go from here
      1m 2s

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