In this video, I want to give you a quick introduction to JavaScript. And here we assume that we have coded before in other language. And JavaScript is not a very different from other language with the same conditional and the same statements, and uses the same paradigm. So different from HTML and CSS that are languages that you can use to mark things or to change the styles. JavaScript is a full functional language with variables, functions, constants, and everything. And we're going to use JavaScript in order to change your page based on the data or based on some interaction of the user. So we have HML and CSS that the look and feel of our page. And then now we going to use JavaScript should change those two elements in order to change how the page looks. And the first thing that we have in JavaScript is how we restore the values. So JavaScript in different versions and browsers want to support different version of JavaScript. So for example here, I am using a keyword name var then the name of a variable and then the value that I want to store in this variable. Variables can store values that's going to change throughout the application. And var is a old keyword, so it's used from the previous versions of JavaScript. And after you release this, they changed this name to let. We're still having var and they have very subtle differences when we use each other. But the recommendation is use always let if you're using a newer version of JavaScript. And if you have to support older browsers, then you're going to have to stick with var. Another option are constants, and constants are declared using the key word const, the name and the value. Constants are not expected to change through all the applications, so they are fixed. And for example here, I have the version of my application and the version is not expected to change while the application is running. So that's why we can use our constant and then just use this name anywhere else in the application. So if in the future, we'd release a new version, we just have to update the constant. Once we have the variables, our way to combine those variables is by using operators. So if those variables are numeric, we can use that each operators to do math operations with them. So, for example, here I have the 3 and the 2, and I have the operator plus between them. And it's adding those two numbers together and assigning the result to the variable result. Another option is to use a shortcut that in this case, we have the operator +=. And what it's doing is saying that the variable result is going to receive whatever value of result plus the number 4. So for example, if the previous result was 5, now result is going to have the value of 9. And I can use the same operator, in this case, plus with strings. And in this case, it's not really a math operator, but now the operator changes the meaning to concatenation. So what do operation does depends on which type of values I am using with those operators. So, for example here, the plus will concatenate those two variables. So if I have the firstName of a person the first variable and the lastName of person the second variable. The plus it going to add those two making the full names of the person. We have multiple arithmetical operators. So for example here, we have the plus for addition and the minus for subtraction. Then we have asterics for multiplications, and slash for if we want to do a division. Another type of operator are the logical operator. Those operators when dealing with two variables are or many variables, you're going to return a value that is either true or false. So for example here, I am checking if the value of 3 is greater or equal to 2, that in this case is true. And the variable result is going to receive this value that is true. Another option is to compare a variable with a number. And for example, here I'm checking if the number that is stored on the variable months is equal to 4. And here I'm using three equals, and it's important to keep in mind that we also have an option of using two equals. So one equal is actually for assignment, then we have two equals that allows us to compare two values. But in this case, we're going to do what we call type casting and convert types in the process and that sometimes can result in unexpected behavior. So it's recommend that you always use three equals that in this case it's going to make sure that the value is the same and also the type is the same. Once again, we have different operators for conditions. And in this case, we have for example, equal that is checking if two values are the same. But we also have the exclamation with two equals that check if two things are different. And then we have the greater than and less than that allow us to compare numbers and check which number is bigger than the other. Another important thing is that, throughout the application, some code, we have to run many times. And one way to do that is to actually create what we call functions. And functions will restore some block of code that we can run later, if we need, by just providing new parameters. So, for example here, I have a function called add. And the function add has its name, that is add. And then we have between parameters that these functions can receive. And here we have v1 and v2. The function then inside the bracket, we have the code that's going to run using these formation, to return something else. And for example here, what I'm doing is that, I'm just adding those two variables and returning the result. A short term rotation of declaring a function is called arrow function. And in this case, we declare a function as a const. We have a const and then we store the function on this const. And in this case, we have equal then we have the parameters to our functions. And then we have this arrow that is unequal and the sign of greater than, that's going to lead to the block of the code. And in this case, since I have only one line, I don't even need the return keyword that I had in the previous version. So the system knows that the result of this addition is going to be returned as a result of the function. Again, there is a subtle difference between those two functions, but in most of the cases, the error function is going to be the function that we can use. But in some cases, we may need to use the previous notation due to some context that one function is going to receive, and is different when we use the different notation. Finally, if I have the two functions, I can actually call them if I need. And I do that by using the name of the function, that is add here. And then passing the values 5 and 3, that in this case, is going to be used by the function to do the sum. So if I'm passing 5 and 3, I'm going to add those numbers, and the result's going to be 8. So keep in mind that JavaScript is full featured language. And we have support from any other features in the language. And we're going to use this language in order to manipulate. The basic thing is installing values and changing those values. But functions are also important, so we can keep and reuse the same code without having to rewrite them in multiple parts of the code.
