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Cleaning up with string concatenation

From: Foundations of Programming: Fundamentals

Video: Cleaning up with string concatenation

So JavaScript is a weakly typed language. Meaning our variables can hold numbers, they can hold strings, they can hold Booleans, but JavaScript still cares, it knows the difference, and it treats those values differently. Let me show you an example. If I create two variables, foo and bar, and I give them numeric values, the number 5 without double quotes, then I call alert adding them together. I'm using the addition operator, the plus sign. What I'll get will be the number 10.

Cleaning up with string concatenation

So JavaScript is a weakly typed language. Meaning our variables can hold numbers, they can hold strings, they can hold Booleans, but JavaScript still cares, it knows the difference, and it treats those values differently. Let me show you an example. If I create two variables, foo and bar, and I give them numeric values, the number 5 without double quotes, then I call alert adding them together. I'm using the addition operator, the plus sign. What I'll get will be the number 10.

It understands these are numbers. It adds them together. If on the other hand, I create these variables with the digit 5, but inside double quotes as a string and then I use exactly the same code, I'm using the addition operator to add them together, what's going to happen is concatenation, not addition. They are going to put them beside each other and what will be output is 55. This is a behavior you do occasionally want to have happen even when the values in your strings are what we think of as numeric.

So you're working with area codes and phone numbers. You don't want to be in a situation where those will get added to each other and actually have a different number, you want them concatenated one beside the other. Now it might get a little more puzzling, but what happens if you've got one of each? So what happens if one variable is a number and the other variable is a string? Well, what's going to happen is if one is a string, that's going to take charge. You'll get concatenation will occur. Now where it can get even a bit more involved is what happens if you try and do something that just doesn't make sense.

We create a variable foo = 5, we create variable bar equal to the letter B, and then we try an alert foo times bar, foo multiplied by bar. Well, concatenation it doesn't work here. What you're actually going to get is this. You're going to get the value uppercase N lowercase an uppercase N lowercase N. This is Not a Number. That's how JavaScript will represent something that just doesn't make sense, and JavaScript has this built-in idea of something being Not a Number. It's something that it understands and this can come in very useful for us.

Because sometimes we have variables that we want to be a number, but aren't. Let's say for example we've got a variable equal to the string 55, so it could be numeric, but it could be abc. It could be an exclamation mark. Perhaps we're asking somebody to type in a value into a prompt box. We hope it's a number, but it might not be. Well, what I can do first is I can create a new variable. I'll call it myNumber. I'm going to try and convert whatever is in foo into a number.

Sometimes that will work, sometimes it won't. So value like 55, it would work. If it was an exclamation mark it wouldn't. Now this looks a little odd. This is a built-in function in JavaScript called Number. It's one of the few times we've seen an uppercase N here. We're passing in the variable foo and we're saying make it a number and store the result in the myNumber variable. Hopefully, this will work, but it might not. So the next thing that I need to do is check it and we use another built-in JavaScript function called is Not a Number, or isNaN.

So isNaN is a built-in function in JavaScript. It accepts a variable and it will tell us, is this a number or is it not a number? Now think about what it's called, isNaN is not a number. What that means is we'll get true or false back from this. It will return true if this is not a number, and because this is in an if statement here, that's what we're asking if it's not a number, we're going to pop up an alert message. Now quite a lot of the time what you want to actually ask is if something is a number.

Well, there is no isNumber function. they can only tell us if it's not a number. So if I'm asking if something is a number, I'm actually going to do a weird double negative here. I'm going to use the exclamation mark to negate the call to the function. What I'm asking is if it's not not a number. Meaning is it a number? In which case we'll then pop up the alert box saying, yes, it's a number. Looks a little strange, feels a little strange,if it's the first time you've seen anything like this, but you'll find JavaScript has a few of these little things tucked away.

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This video is part of

Image for Foundations of Programming: Fundamentals
Foundations of Programming: Fundamentals

61 video lessons · 92784 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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