Previously, we talked about three friends type variables, we talked about objects. And we also talked about arrays. Now it's time to talk about functions. Functions are an essential part of JavaScript, because they are one of the building blocks of JavaScript. And what a function is, is that a few line of codes that perform a specific task. So for example, if you want to calculate the time or the temperature, or do something, you just create a function that will do that for you, instead of writing just codes, just random code that would do nothing.
And the name of the function are always so clear, and gives you an idea of what this function does. So for example, Have a function could be get temperature, get time, calculate time. So when you read when you read the name of the function, you immediately know what this function does. So let's now create a simple function to create a function in JavaScript, you would just type function and then the name of the function. So for example, we want to multiply a number by two so I'm going to give this function a name of multi ply by two and then I'm going to add is he's always add parentheses at the end of the function and in curly braces, and inside those curly braces, you are going to add what this function does. So what this function does is that it is going to multiply by two.
So for example, I want to multiply var a Equals Three multiplied by two, multiplied by two. And then I'm going to print this on the screen by using console dot log. And I'm going to just add, I'm going to pass the eight inside the console log. And if now I save and execute our code, nothing will happen. And the reason is that functions will not be executed, this line of codes will not be executed unless you call a function. So the difference between a function and a simple code is that a function we just combine these codes together, that will perform a specific task.
And whenever whenever you want to perform that task, you need to call that function. So to call a function, you just type the name of that function. So here I'm gonna type the name of the function and then parentheses and then semicolon. Now, what you did is that you called this function. So if now I save and run, as you can see six has been printed on the screen. But as you can see this function is not meaningful enough.
So instead of just using this, I'm going to pass something to this function. So I'm going to pass for example, I am going to pass a variable called B. And I am going to change this var from from A to result result. And I'm going to multiply this number that I have passed which is B by two by two, b multiplied by two. And then the result is going to be printed out on the screen. And here when you call a function, you pass any number you want.
So for example, I want to pass the number four if now Save and run our application. As you can see, I get the result of eight, because I passed four, which is B, and B has been has been multiplied by two. And the result is now eight and eight has been printed out on the screen. So now this function is very meaningful, then the name of the function multiply by two, and we can pass a number. So any number you pass, for example, if now you pass five instead of four, and if you save and execute, you would get 10. Because any number you pass, you can multiply it by two.
So this is how important functions are in JavaScript. And as you can see, they are very, very meaningful, because later you will see how important they are. When you want to do a specific thing in your application. You would just need to call the function instead of writing the code over and over and over again. You just write the code once and every time you need to execute this code you just call the function with a single line of code.