--- title: Intro to Values and Types in JavaScript slug: intro-to-values-and-types-in-javascript published_at: 2020-08-31 01:54:54 +0000 updated_at: 2026-03-04 20:14:49 +0000 summary: description: In this edition, we'll start from the very basics and talk about what values and types are in the context of programming. These concepts are covered at a high level, then we show some examples and talk about commenting code in, commenting code out, evaluating expressions, and reading error messages. @cjav_dev on Twitter tags: [computer science, beginner programming, programming, values, types] views: 702 author: CJ Avilla url: https://www.cjav.dev/videos/intro-to-values-and-types-in-javascript youtube_url: https://www.youtube.com/watch?v=LhMPRWOtdZ4 youtube_id: LhMPRWOtdZ4 embed_url: https://www.youtube.com/embed/LhMPRWOtdZ4 thumbnail_url: https://i.ytimg.com/vi/LhMPRWOtdZ4/hqdefault.jpg type: video --- # Intro to Values and Types in JavaScript *Published: August 31, 2020* *Views: 702* ## Watch [Watch on YouTube](https://www.youtube.com/watch?v=LhMPRWOtdZ4) [![Intro to Values and Types in JavaScript](https://i.ytimg.com/vi/LhMPRWOtdZ4/hqdefault.jpg)](https://www.youtube.com/watch?v=LhMPRWOtdZ4) ## Description In this edition, we'll start from the very basics and talk about what values and types are in the context of programming. These concepts are covered at a high level, then we show some examples and talk about commenting code in, commenting code out, evaluating expressions, and reading error messages. @cjav_dev on Twitter ## Transcript a computer program is a list of instructions that can be followed by a computer to perform a specific task most programs work by taking some input data processing that and creating some output data understanding the values and types will form a foundation on top of which we can build up concepts that will allow us to write our own programs so values are the actual underlying raw numbers and text our program manipulates tony stark the number 43 and false are all examples of values sometimes we'll say that when we literally write the number four and then the number three next to each other to form the number 43 that we're writing the literal 43 same with tony stark if we write the quotes then the letters t o n y etc into our code we'd say that we're using the string literal tony stark sometimes we might say that this is hard coded meaning that when the program runs the literal value isn't going to change literal values are used a lot when you're first starting out but eventually data will likely come from a database or some user input every value belongs to exactly one data type the kinds of values that can be represented and manipulated in a programming language are known as types all of these literals that we've written so far can be categorized as a specific type we see string number and boolean those are the types for tony stark 43 and false most languages use a very similar list of super simple types like a collection of characters as a string of text a list of digits with or without a decimal point as a number and then some type for representing true and false some programming languages will have more types that they have built in other programming languages will have a very small set of these primitive built-in types that you are to use to build up to more complex types when a program needs to use a value again in the future it assigns that value or sort of like stores that value in a variable variables have names and they allow us to use those names in our programs to refer back to the values we'll talk more about variables later here we're assigning the value 7 a name age we're also assigning the string grayson to the variable name first name if we wanted to print out the value 7 using the variable age we might call some print function and pass in the variable name or the literal number 7 and we'll take a look at how to print out the number or the string or whatever value it is in different programming languages there's really two different kinds of types there are built-in types and then there are user defined types built-in types are the types that come with the language this is the batteries included stuff like numbers and strings and dates and arrays and object types user defined data types are defined in terms of built-in data types and other user-defined data types here we're defining a student type or we have defined a user-defined type called a student type which is composed of or made up of other built-in types the number for the the age and the string for the first name we might also create a car type which takes in a make and a model both of which might also be user defined types typically a programming language does not let the programmer extend or redefine those built-in types next a type can either be mutable or immutable these primitive types like 7 and true are immutable meaning they cannot change you can change the value of the variable meaning you can change what the name of that variable is referencing by pointing the variable at a different value however there's no way to change what the number seven means when we talk about the number seven there's no way we can like modify the number seven to be the number eight or the number six we wouldn't want to change what the number seven means similarly with true we wouldn't want to change what it means for something to be true a mutable object can change here we have an array or a list and this list has four values it has 9 10 9 and 11. these might be ages or these might be other values but the the underlying type for this collection of values is called a list a list or an array in some languages can change all right today we're using reple to run some of our javascript code on the right hand side we have the terminal output window in the middle we have our editor we're modifying the index.js file today and we have line one right now there is no code in our index.js file so when we run the code nothing is going to output and that's fine the very first thing i want to do is talk about how we can create some output how can we make something show up in the terminal so in in javascript we do that using a a method on the console called console.log so we type out the word console followed by period and then the word log and then we have an opening and clothing opening and closing parentheses and inside of those we can put in whatever we want to actually print out to the console so in this case if we just put the number one and click run we will see the output of number one in the console the next thing i want to talk about is adding comments to your code in javascript we can add a comment by prefixing a line or prefixing the comment with slash slash comments are generally used to describe bits of your code and to make it easier for you to remember what code is doing when you go back to refer to it later but for this example i'm going to use commenting to disable parts of the code so that we can keep them around for reference later so i've added a slash slash to the beginning of our line 1 here which is printing out the statement 1 and because that's been removed if we try to execute this there is no code that will run because the only code that we have here is commented out and a comment represents some text that describes the code but is going to be ignored by the javascript interpreter all right so the next thing we'll do is console.log the number from the example that we talked about earlier and that is 43. so well console.log 43. note that at the end of my console.log statement here i could put a semicolon which is sort of like a period in javascript it ends the statement it's not necessarily required but it is helpful to denote the end of a line so i'm going to leave them out for now but just note that some javascript you'll see semicolons and it is good practice to have them in there but they're not required so we're console logging the number 43. let's move on to the next example where we talked about printing out tony stark okay if we if we pass in the words tony and stark to our console.log statement we might expect that this will log out tony stark unfortunately we hit an error uh something is wrong here and so let's let's go take a look at this error message that we're seeing in the console and try to decipher this and see if there's anything helpful that will help tell us how to fix our code so we see where the code is running it's in index.js and then we have a colon and a number after it this colon and then number tells us what line number the the error is on so in this case it's in the index.js file on line three so if we look at our line three here we have console.log tony stark and we have a bunch of arrows pointing at tony and it's a syntax error missing um missing closing parentheses after uh argument list and so it thinks that tony was the argument and that we were supposed to like put a closing closing parenthesis there but it turns out that this the error is actually because javascript doesn't know where the string begins and where the string ends so the way that we tell the javascript interpreter where the string begins and ends is with quotes so we're going to add a single quote at the beginning of the string and a single quote at the end of the string it turns out that javascript works with both single quotes and double quotes so if we wanted to replace this with double quotes we could do so and it would work exactly the same there in es6 there was recently a recent edition where we can use these back tick style quotes also for strings so you might see those so there's like three different at least three different ways for now we will just use single quotes but something that i wanted to point out is that if you have a single quote at the beginning and a back tick at the end or maybe a double quote at the end javascript won't know that this is a string the the beginning quote and the ending quote need to be the same kind of quote so you need a single quote at the beginning single quote at the end earlier we talked about another kind of data type which is a boolean so let's look at how we can log a boolean value so we say console.log true and that will print out true same with false pretty straightforward stuff true and false represent just like those boolean yes or no values next let's talk about how expressions are evaluated with these literals so if we have the number literal 43 and then we use the plus operator we can add some value some arithmetic values together to get a a specific output so if we take the number 43 and add it to 10 we'll get 53. so what's happening here when we run this code console.log 43 plus 10 is the javascript interpreter will first evaluate this expression so we'll take 43 and add 10 to it and sort of replace what what we've highlighted here with that resulting value so 53 will replace 43 plus 10 and then 53 is what's passed to the log method on the console object so we have evaluated this expression 43 plus 10 to get the number 53. let's also talk about um how the plus operator might operate on strings so if we have the string tony and we add it to the string stark this will there is no like arithmetic operation that you can do to add the word tony to the word stark right and so strings the string type will behave differently with the plus operator in this case it's going to take the string on the left and try to add it to the string on the right so it's going to concatenate these two things concatenation is the linking of things in a series so we're going to try to link together the string tony with the string stark and we should get back tony stark so if we run this we'll see the output here tony stark note that there is no space between the first name and the last name we have tony stark with no spaces so one way that we could add the space between the first and last name is by simply just adding a space to one of the existing strings tony space plus stark that would give us tony stark with spaces in the name another alternative instead of adding the plus directly to the first name we could add the plus as a third string that we're concatenating together so tony plus a space plus stark okay so these are two different ways that we can concatenate strings together to evaluate the name tony stark sometimes it can be helpful to know the type of object you're working with or the type we're working with in javascript it has a really handy built-in function that you can call called type of so we can say console.log type of and then pass in some value in this case we'll pass in one you can also pass in a variable and this will tell you the type of that thing so in this case we're passing in one and javascript tells us that is a number that's fantastic if we do the same thing we pass in type of and we just passed the word tony as a string with quotes again we will get back and see that this is indeed a string you see that it is a string so typeof is one of the ways of inspecting your value to see what data type that value is you --- [Back to all videos](https://www.cjav.dev/videos) --- ## Hey Agent, thanks for visiting! 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