JavaScript Variables


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JavaScript Variables

  1. 1. JavaScript Variables Charles Russell Bennu Bird Media
  2. 2. Statement and Expressions ● A Statement requests an action. ● An Expression sets a value. ● Variables are used in both ● They are passed into functions and used to control branching and iteration ● They can be the target of the expression or the value of the expression – In computer books you may see L value and R Value when referring to expressions
  3. 3. So What are they ● A variable a just a place to put things you want to use later. A good anology would be a box ● In JavaScript anything can go into a box ● In this language the boxes are a little magical – Boxes can resize themselves to hold anything you put in them. – Dumping from one box into another makes what was already the box you are dumping into vanish
  4. 4. Labeling the Boxes ● To name a variable just type a name and set a value. You will not only named it you have created and sized it. ● var myVariable=“Some really cool stuff“; – Note the var while not required leaving it off has some implications that we will get into later ● Another word for name is identifier and in computer books it is more common to use identifier. ● In general you can use any name you want, but there are a few rules
  5. 5. Whats in a name ● In Javascript a name must begin with a letter _ or $ ● Names beginning with _ are generally used by the system ● Names beginning with $ are commonly used by libraries ● After the first character you can use as many letters and numbers $ and _ as you want after that ● Name are case sensitive Name and name are not
  6. 6. Forbiden Names ● Use of these words as names will cause an error abstract debugger final instanceof protected throws boolean default finally int public transient break delete float interface return true byte do for let short try case double function long static typeof catch else goto native super var char enum if new switch void class export implements null synchronized volatile const extends import package this while continue false in private throw with
  7. 7. Names with Baggage ● Some names are used by Javascript implementations and while legal should be avoided. A partial list is below for more go to alert clearInterval decodeURIComponent all clearTimeout defaultStatus anchor clientInformation document anchors close element area closed elements Array confirm embed assign constructor embeds blur crypto encodeURI button Date encodeURIComponent checkbox decodeURI escape
  8. 8. Weak Typing ● JavaScript is a weakly typed language ● This does not mean that it is type unaware ● This means that you do not have to declare the type of the variable
  9. 9. Summary ● Variables are used in statements and expressions ● The are just a way to store things for later use ● There are rules to names ● You cant use reserved words as names ● Some legal names are not a good Idea ● Java Script is a weekly typed language
  10. 10. Next Datatypes