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So far we've worked with h t AML and CSX.

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We know that both these programming languages instruct our web browser on how our web page should be

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displayed.

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We also learned that HDL and CSX are static languages that do not interact with users.

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In this section of the course we'll be exploring a very powerful client side programming language known

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as javascript.

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When we say client side it means the language communicates with our web browser to allow user to web

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page interactivity client side languages differ from server side languages such as BHP which will cover

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later on server side languages communicate not with the web browser but with a web server.

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JavaScript can be used to implement many different types of interactive features on a web page.

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Let's take a look at some examples of JavaScript functions that interact with users

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this javascript code calculates the amount of characters a user has typed into a text area.

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Once you type in the line of text and press to calculate characters button you'll see that this line

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of text has twenty three characters

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this javascript code displays an error message.

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If more than 10 words were typed into a text area

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this is the pop up alert that appears if more than 10 words are typed in

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this javascript code validates a form to make sure that the required fields were completed.

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I purposely put an incorrect email address and left the other fields blank these fields are required.

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So once we click submit we receive an error message saying that some of the required fields were not

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completed.

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This is done using JavaScript validation will score much more advanced validation techniques than this.

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This is just a basic example

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this javascript code ensures a user agrees to the terms and conditions of a web page in order to submit

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a form

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if I do not check off this checkbox here.

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You'll notice I get a pop up message saying that we must check the box to continue.

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And again this is another javascript function.

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This is a slightly more advanced script.

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It's a tic tac toe game and the purpose is to line up the x's or O's all in one straight line diagonally

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horizontal your vertically

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and so you can see if you lose a pop up message appears indicating that the game is over and you've

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lost.

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These are just a few basic examples of what JavaScript can be used for.

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Javascript does have some limitations.

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We've already touched on one in that it cannot be used to communicate with the web server.

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Javascript cannot be forced onto a user's web browser either.

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Remember javascript is a client side language meaning if your user has turned off javascript support

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in their web browser your script will not work.

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Also if the user's web browser is outdated it may not allow certain JavaScript functions to work correctly.

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Note that almost all modern web browsers support javascript by default when installed.

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Many people also confuse javascript with Java.

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Note that these are two languages and they are not the same.

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Java is a much more powerful and complex language in the same category is C and C++

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javascript is an object oriented language.

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This means that attributes of an object are contained within variables.

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For example if we want to describe a person will refer to this person as the object we would typically

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use attributes such as name height weight gender and age.

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The values of these attributes will vary or differ from person to person.

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Another word for attributes is variables.

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These variables will contain the values for each person as we progressed through this dissection.

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You'll gain a better understanding of this concept and the importance of working with variables.