Welcome back to NBK Tech World. This lesson will be a review of everything we've done so far. If you already feel comfortable with all the previous lessons you can skip this video. Otherwise let's keep on going. So going back to the beginning of the course we learned that every major browser contains a browser console and in my case right now I'm using Firefox we can open up the console and we can type JavaScript commands here and we have an interpreter that will give you the result on the spot. So the first thing we learned how was how to print a message to the console. We learned about the console object that has a method and that method is called log. So remember when we have functions functions do something they take some input they do some processing and they return give you back some output that's the general idea of functions. Now we learned also that when we have a function and when that function belongs to an object in this case the console object we can call that function a special name called method. So you might hear the terms function and method used interchangeably but there's that slight difference. So if the function is by itself and it's not tied to any object it is not really a method but if it is tied to some object you can call a method. Anyways let's keep on going let's do the review. So essentially the function will take an argument which is kind of the input so you have to tell it what to print to the screen. We can just print any message we want using a string. A string is a set of characters enclosed by quotes. By convention I'm using the single quotes convention but mind you there are other types of quotes like the double quote and the back ticks and they all have slightly different behavior we haven't really learned in detail about those but just keep in mind anything under quotes think about strings okay. So the function will produce this print out to the console with whatever you gave as a string here. So in this case we got hello world. Alright so that's how we started then we learned about the concept of variables to store information. So we can define or declare a variable and then define it with a value in two ways and the first way is with a const keyword. We can define for example a variable called name and to that let's assign a string to it. Let's call it whatever your name is. I will just call it my name. Right we learned that this string will be stored in this variable called name and because we use const that value can only be assigned once. So if I try to change name like this some other name we're gonna get an error because in violet assignment to const and that's because the const if you define declare variable const it will only allow you to assign a value once. If you want to be able to change the value of the variable name again like I tried to do here you have to use another keyword and that's the keyword let. So if you say let for example let's create another variable called age. I'm gonna give an arbitrary number okay. So let age be 35 so the variable age contains the value 35 which by the way is what kind of type in JavaScript that's a number okay. It's not within quotes it's just a number by itself so it's type of number okay. Remember type of operator you can type type of and putting whatever you want to find out the type of and it gives you a number. So we also learned that right. So going back to the let if I try to change age to something else like 23 notice that now it works there's no error like before and if I see what's inside age it's exactly 23 the new value. So that's because we use the word let. So if you want to change be able to change assign the value to the variable age more than once not just the first time like we did here you use let. My advice is to always start out with cost and if later as you program and do more add more code if you feel that's necessary for the variable to be changed you should change the cost to let in the declaration. Alright so that's it for variables and then we talked about the numbers and operations on the numbers basic math that kind of stuff. So I'll be pretty quick with that I think you got the point we can do mathematics here right on the console 23 minus 11 gives you 12 and 20 divided by 5 gives you 4 7 times 3 21 and you can do addition 9 plus 2 11 right. We learned about parentheses if you have 3 times 4 plus 8 but if you do it like this because of the precedence of the operators the 3 will multiply 4 first if we actually intended for the 4 to be added to 8 first you would have to add the parentheses right. That's where you're forcing the addition to be the first thing they'll be 12 and then you do 3 times 12 which is 36. If you didn't have that right you're going to get something else because the multiplication always takes precedence over addition. So we get 12 plus 8 which is 20 totally different value right. We also learned about some things like if you try to divide by 0 what do you get you're gonna get infinity if you take a number that's non-zero and divide by 0 but if you take 0 and divide by 0 you get NAN which means not a number okay this is not a number. So if you just type off let's see what we get. So 0 divided by 0 wow it's type number okay all right so whoops I accidentally open the other window that continue your type of to find out what the type of this guy is you can see is also a number so both these guys seem to be a number okay so you have hello well and if you have a number within strings it's actually strings not really a number so we learn also about that because 3 is not really equal to 3 if you use the triple equals operator right because the triple equals the strict equality it compares not only the contents but also the type of each operand operand is whatever is next to the operator here so in this case the slap hand side operand 3 so 3 this is a number there's no quotes and on the right hand side there's a number but it's within quotes so this guy must be a string but a string is not really a number so this guy is strict equality saying it'll be false but if you have double equal equals that's not so strict so it's actually going to give you what is 3 equal to the string 3 it's going to be true because it only compares the contents it tries takes this guy okay let's try to make it a number because you have a number of things strings so it tries to convert to a number and it succeeds because it's just a number under quotes and it's actually equal in content even though the type is different we have a number on the left hand side we have a string on the right hand side so we learned that about those kind of comparisons and can use other kinds of operators uh greater than greater than or equal to less than less than or equal to we also learned about the strict inequality right which is the opposite of the triple equal sign if you want to check if something is not equal to another thing in a strict fashion okay