JavaScript Basics

            Unlike most programming languages that allow you to define a variable as an int, double, etc JavaScript only allows for you to declare a variable as var. This means that whenever you give the variable a value, JavaScript usually decides to hold the value in a String, mean it would be considered almost a word. So if you did 2+2, you would get 22 instead of 4 since the "+" sign with two strings means to simple put them together. There is an example of this on the example page for this section. For example the assigning a value to a variable would look like this: var num1=2; But if you did this: var num1="2"; that now means that number two is being held in the variable as a string (like a letter, or word would be), the same way as, "two", would be held in another variable, but just becuase you enter a number in digit form dosn't mean that JavaScript will regonize that it is a interger or a String. What you must do to ensure that JavaScript knows what type of variable is being passed in, other than a String, is parse it This is usually done only if JavaScript will not regonize the data type, an issues that is uaually run into every so often. What this means is you want JavaScript to turn the in comming value into eahter a: Integer/Double or boolean , to name the major variables that will be used. The syntax looks like this for turning/making sure a variable is a integer number: parseInt(variable); There are examples shown on the example page for futhur clarification.

            There is also a type of variable called a Global variable. This variable is really no different then all the others, EXECPT that it is visiable to all of the functions in between the script tags (<script>), not inside of a single function. When a variable is inside of fuction, that means that the variable is only visible INSIDE of that function, thus it's Scope is only in that function. When declared outside of all functions though, the variable has a global scope.

            You should also know that just about everything you do in JavaScript is done inside of a function or multiple functions. A Function is a block of code that can be called over and over again to perform a specific task. So say you make a function to take numbers from 3 different fields and add them all together. The function would allow you to call it every time someone that the total button, and thus would add all the values from the provided fields, add them all together, and then if you wanted to, you can display the total (shown in more detail on examples page). Another very important bit of information to know is that, HTML and JavaScript work together by using EVENT HANDLERS. These event handlers, like the name suggests, handle events. An even can be something such as; a mouse click, a mouse over, when the page loads, etc. The event handlers allow you to tell the page what function to call when certain event takes place. Such as a button being pressed, going back to the previous example, it will then call the function you tell it to, and perform the task you programmed the function to do. You may also pass values to functions, all you have to do is place a variable in between the () and when you call the function in the event handler, just have the value you want passed up in between the () of the function call.

Go here see more examples and see further explanations on Basic JavaScript.

JavaScript Document Object

            The document Object is probably one of the must used objects in JavaScript. It is used from writing to the document, to getting the attibutes of every instance of a tag on the page, thus allows basic changes to be made. Though there is really not much to say about the document object, it is good to know what it's able to do on the web page.

Here is a comprehensive list of document Document Object.

JS Loops

            Although "if" statements and variables are very useful, it would be very difficult to write a program with only those tools at your disposal, especially when it comes to tasks that repeat themselves many times over. That is where loops come in. Loops allow you, the programmer, to execute a section of code as many times as needed to in order to perform a certain task. For example, let's say the user wants you count to a specific number that is specified by the user. So what you have to do, say the user inputs 20, is count 1 to 20 in sequential order, displaying each number on the page till you get to twenty. Not knowing the upper limit of the numbers they could enter or what number the user is going to put in makes the program interesting, but not having a data structure that can repeat itself would make this problem nearly impossible to solve.

           That's where loops come into play, and there are 3 different kinds, the "while loop," the "for loop," and the "do loop." The first one we will talk about is the "while loop," which essentially means, continue while a certain condition is true. The syntax looks like this: while (<condition>){}. Remember that just like the "if" statement loops only need curly braces ({}) if there is MORE THAN ONE LINE of code that goes inside of that loop. A while loop in our situation could be used to take a variable that is a number and increase it from 1 till it is greater than 20. The syntax would look like this: while(someVar<20){do something}.

           Next is the "for loop," which is usually used when you, the programmer, knows how many times the loop needs to reiterate. The syntax for the "for loop" looks like this: for(declareVariable<condition>incrementDeclareedVariable){}. A "for" loop in our particular situation would be very handy since we will know how many times the loop is going to execute. In other words, even though we DO NOT know what number the user is going to put in, we do know that the loop is going to have to execute a certain number of times based on what the user enters into the program.

           Finally there is the "do while" loop, which will execute at least once, even if the condition is not met. The syntax for the "do while" loop looks like this: do {(code)}while(<condition>); Notice that the "do while" loop is the only loop that has a semicolon (;) after the condition. For our example a "do while" loop WOULD NOT BE be very useful because if the user enters zero, then the "do while" loop would still print out 1.

           As can be seen, loops are very helpful and are extremely important when it comes to programming. These loops are all very useful in different ways in different circumstances, it just takes time and practice to learn where, when, and how to use them. Also remember that in loops, you use the same compairsons as you would use inside of an "if" statement.

Here is more explanation on Loops in JavaScript.