Variables and usage
Variables are like storage units. You can create variables to hold values. It is ideal to name a variable something that is logical, so that you'll remember what you are using it for. For example, if you were writing a program to divide 2 numbers, it could be confusing if you called your variables numberOne, numberTwo, numberThree because you may forget which one is the divisor, which one is the dividend, and which one is the quotient. A more logical approach would be to name them just that: divisor, dividend, quotient.
It is important to know the proper syntax to which variables must conform:
- They must start with a letter or underscore ("_")
- Subsequent characters can also be digits (0-9) or letters (A-Z and/or a-z). Remember, JavaScript is case-sensitive. (That means that MyVariable and myVariable are two different names to JavaScript, because they have different capitalization.)
Some examples of legal names are Number_hits, temp99, and _name.
When you declare a variable by assignment outside of a function, it is called a global variable, because it is available everywhere in the current document. When you declare a variable within a function, it is called a local variable, because it is available only within the function. Using var is optional, but you need to use it if you have a variable that has been declared global and you want to re-declare it as a local variable inside a function.
Variables can store all kinds of data. To assign a value to a variable, you use the following notation:
dividend = 8;
divisor = 4;
myString = "I may want to use this message multiple times";
message = myString;
Let's say the main part of the function will be dividing the dividend by the divisor and storing that number in a variable called quotient. I can write this line of code in my program: quotient = divisor*dividend, and I have both stored the value of the quotient to the variable quotient and I have declared the variable at the same time. If I had wanted to, I could have declared it along with my other assigned variables above, with a value of null. After executing the program, the value of quotient will be 2.
It is important to think about the design of your program before you begin. You should create the appropriate variables so that it makes your life easier when you go to write the program. For instance, if you know that you will be coding a lot of the same strings in a message, you may want to create a variable called message and give it the value of your message. That way, when you call it in your program, you do not have to retype the same sentence over and over again, and if you want to change the content of that message, you only have to change it once in the variable declaration.
It is important to think about the design of your program before you begin. You should create the appropriate variables so that it makes your life easier when you go to write the program. For instance, if you know that you will be coding a lot of the same strings in a message, you may want to create a variable called message and give it the value of your message. That way, when you call it in your program, you do not have to retype the same sentence over and over again, and if you want to change the content of that message, you only have to change it once in the variable declaration.
