Operators and Expressions JavaScript topics covered:

  1. Assignment:

    The equal sign (=) is the assignment operator.
    To set a variable called myNumber to the value of 100, the code would be:
    myNumber = 100;

    ** Note the variable that receives the value is always on the left **

    Arithmetic Operators: Used to perform mathematical calculations. 
    operator		Symbol
Add and assign	+=
subtract and assign	-=
multiply and assign	*=
divide and assign	/=
modulus and assign	%=

  2. Addition:

    Assign returnValue the sum of x plus y.

var x,y,returnValue;
x = 30;
y = 40;

returnValue = x + y;	//returnValue = 70
x = x + y; 		//x now contains the value 70, y remains at 40
y = y + 100; 		//y is now 140

Using the assignment operator
x += y; 		//x now contains the value 70, y remains at 40
y += 100; 		//y is now 140

What happens when you assign a variable a string and add them together? 
The values are concatenated.
a = "2";
b = "3";
returnValue = a + b; 	//returnValue = 23

  3. Converting Data:

    For data that you aren't sure is numeric or a string you can convert the string to a number using parseInt() or parseFloat() be carful when using the eval() function click here to see the demo

    What happens when the variable you are using does not contain a number? The previous example was changed so x would contain the string "stuff". When using the eval() function, an error is displayed and all processing stops.
    When using parseInt() or parseFloat() no error is produced, however you will get an answer of NaN - Not a Number.

    The first part of the demo is commented out because the eval() function keeps the code from processing. To see the demo in action view the source and delete the comments.

    click here to see the demo

  4. typeof() function

    There is also a function to evaluate what is in a varaible. The function is typeof(). This function will be discussed more in chapter 7.
    click here to see the demo

  5. Subtraction:

    x = 30;
y = 40;
returnValue = y - x 	//returnValue = 10
x = x-y			//x is now -10, y remains 40
x -= y			//x is now -10, y remains 40

a="2";
b="4";
returnValue = a - b	//returnValue -2

click here to see the demo

    6. Increment, Decrement, and Assignment:

    prefix and postfix operator click here to see the demo

    Multiplication:

    x = 30;
y=40;
returnValue = x * y;	//returnValue = 1200
y = x * y 		//y is now 1200;
y *= x 		//y is now 1200;

click here to see the demo

    Division:

    x = 12;
y=4;
returnValue = x / y;	//returnValue = 3
y = x / y 		//y is now 3;
y /= x 		//y is now 3;

click here to see the demo

    Modulus:

    When you divide 40/30 you get the value 
But what if you wanted the remainder? 40/30 is 1 with the remainder of 10.
This is where the Modulus operator comes in handy

x = 40;
y=30;
returnValue = x % y;	//returnValue = 10
y = x % y 		//y is now 10;
y %= x 		//y is now 10;

click here to see the demo

    click here to see the convert temperature program demo.