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Input/output and persistence

From: Foundations of Programming: Fundamentals

Video: Input/output and persistence

Programming is all about input and output, but what that means has changed over the years. You go back a few decades and the idea was simple. The only programs we used were what were called batch programs. You started the program like it was a food processor. You'd be giving a file of data for input, you'd let the program process all of it and spit out the results to another file or even directly to the printer, and then the program stopped. You did not interact with the program as it was running. The closest thing to this for most people now is a few command line programs or the occasional utility like doing a full virus scan of a hard drive.

Input/output and persistence

Programming is all about input and output, but what that means has changed over the years. You go back a few decades and the idea was simple. The only programs we used were what were called batch programs. You started the program like it was a food processor. You'd be giving a file of data for input, you'd let the program process all of it and spit out the results to another file or even directly to the printer, and then the program stopped. You did not interact with the program as it was running. The closest thing to this for most people now is a few command line programs or the occasional utility like doing a full virus scan of a hard drive.

Things which are designed to run and finish as fast as possible, but instead the shift is to programs that run with graphical user interfaces. Things like a web browser that don't just start and run all the way through and stop as quickly as possible, but they are programs that stay up. We can interact with these continuously and unpredictably over hours or even days or even weeks. And with these input and output is a bit vague. Well, yes, a mouse-click is input, something typed in a webpage is input, and changing an image on the screen is output.

But that doesn't really feel the same as saving and loading files, because sometimes we still want to be able to save documents to the hard drive or load files from the hard drive or save information to the web. So describing just everything as input and output becomes a little generic. So when we talk about really saving information, running a program that then saves information to our documents folder or saves to a database or saves to the web or saves to a cloud, and I mean data that outlives the currently running program, meaning that we could close the program and that data would still be on the drive or in the database or in the cloud, then we use the term persistence. And we also refer to this as saving the state of a program. Because without deciding to persist, our data it all just disappears.

All the variables we've worked with so far are just stored in the computer's volatile memory in RAM while the program is running and when we close the program everything is gone unless you plan otherwise. But here's the issue. Different programming languages support persistence in different ways and JavaScript not very much at all. There are no words in JavaScript to save a file to the Documents folder. You can't do it. Now that's by intention. JavaScript was designed to be embedded in webpages. You just don't want all the webpages you've ever viewed being able to save files directly to your hard drive.

So for security those words were never built in to the JavaScript language. Now languages that are more geared to desktop development or mobile development or even mainframe development do have built-in ability to write code to save or load files to the hard drive. They often have a variety of different words to do this and we'll talk about a few of these features shortly, but first let's take a look at what JavaScript does like to do for input and output if it can't load and save files.

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This video is part of

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Foundations of Programming: Fundamentals

61 video lessons · 96174 viewers

Simon Allardice
Author

 
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  1. 4m 15s
    1. Welcome
      1m 17s
    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 48s
    1. Building with the if statement
      7m 35s
    2. Working with complex conditions
      4m 9s
    3. Setting comparison operators
      6m 59s
    4. Using the switch statement
      6m 5s
  6. 17m 54s
    1. Breaking your code apart
      4m 1s
    2. Creating and calling functions
      2m 56s
    3. Setting parameters and arguments
      6m 7s
    4. Understanding variable scope
      2m 23s
    5. Splitting code into different files
      2m 27s
  7. 13m 31s
    1. Introduction to iteration
      4m 28s
    2. Writing a while statement
      5m 24s
    3. Creating a for loop
      3m 39s
  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 58s
    1. Working with arrays
      5m 46s
    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 25s
    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 2s
  13. 14m 16s
    1. Introduction to object-oriented languages
      5m 18s
    2. Using classes and objects
      6m 28s
    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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