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We touched on variables in the introduction of this course.

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Variables are a very important concept to understand when it comes to programming in any language including

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javascript unlike javascript constants.

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Variables are named containers that can store a single value or multiple values.

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These values can change based on user inputs or other factors.

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Let's take a look at a basic example of how variables can be used to store values

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in this javascript code.

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We've declared three variables.

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Variable X Y and Z.

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You can think of each variable as a container the variables each contain their own value the value of

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variable x is 10 the value of variable Y is 15.

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The value of variable z is equal to the sum of variable x and y.

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Which in this case would be twenty five or ten plus 15.

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Now let's output the value of c Using the get element by IED output method will output the result in

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a paragraph with the IED.

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Demo

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now let's save our file and preview it in our web browser to see the results.

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Here we can see our heading javascript variables in our paragraph working with variables and underneath

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that we can see the result has been output.

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So variable X has been added to variable Y and the result has been output it to 25

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in our example the X Y and Z name we attach to the variable are known as variable identifiers.

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Each variable you declare must have a unique identifier we used very short identifiers but as we progressed

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through the course we will be using more descriptive identifiers for example color shape size age and

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weight these would all be considered more descriptive.

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There are some general rules when selecting identifier names names can contain letters digits underscores

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in dollar signs names must begin with a letter names are case sensitive.

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Reserved words like Javascript keywords cannot be used as names.

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Javascript variables can hold numbers like one hundred or ten point five or text values for example.

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John Smith

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text values are known as text strings.

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Strings must be written in single or double quotes numbers can be written without quotes.

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If you put quotes around a number it will be treated as a string

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for the sake of this example.

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Let's change our numerical value 15 to a text value.

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Now when we save our file

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and refresh our browser we can see that the numerical value 10 stored within the x value variable

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has been attached to the string contained within variable Y.

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The output is contained within variable Z.

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Which equals X plus Y.