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JavaScript Introductin to Functions
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JavaScript Introductin to Functions


This is the slide show to accompany my YouTube video by the same same

This is the slide show to accompany my YouTube video by the same same

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  • 1. JavaScript Introduction to Functions Charles Russell Bennu Bird Media
  • 2. What is a function. ● As Defined by W3Schools A function is a block of code that will be executed when "someone" calls it. ● Saved for later and use on demand
  • 3. Function invocations ● functionName( parameterList); ● Parameters, or arguments, are the values to be used by the function – Parameters may be expressions, variables, literals, or objects ● Ex: alert('Hello World'); ● Functions may return values – name = fullName('Charles', 'Russell');
  • 4. Making Your Own Functions ● Functions can be constructed two ways ● Statement form ● Expression form
  • 5. Statement form function nameOfFunction(parameter1, parameter2, ...) { //statments and expressions return result; //Optional if no value to be returned } ● The return statement is optional and may or may not return a value ● Immediate invocation optional with () following end of code block ● If a parameter is declared and not passed no error is generated until an attempt is made to use the missing parameter. ● Some functions are selfcontained and need no arguments
  • 6. Functions as Values ● Remember in the discussion on data types ● Anything not a primitive is an object ● In JavaScript functions can be used as values, be passed as parameters, and returned as values from functions
  • 7. Expression form var nameOfFunction = function (parameter1, parameter2, ...) { //statments and expressions return result; //optional if no value to be returned } ● Later we will see that in general this is more useful than the statement form.
  • 8. Scope ● In this Language variables default to global ● This means that any function anywhere can use and overwrite your values at any time ● The var keyword is what is used to limit scope to the function in which the variable was delcare ● There is no block scope only function scope ● This means that any local variable declared in a function can be accessed from anywhere in the function even sub functions ● Variables in parameters have local scope
  • 9. this Keyword ● The keyword this is a special object that refers to different important objects based upon context. ● When a function is created with the statement form and is not part of some other Object this refers to the global Object if ES3 this is undefined if ES5 – For browsers this is the Window Object ● When function used as a constructor this refers to current instance of current function ● When as a method this refers to calling object (normally the parent)
  • 10. Summary ● Function are code ment to be used later ● A function is called by using its name and opening and closing parents surround 0 or more parameters ● Functions may or may not return a value ● Functions are objects and can be used as values (not just the result) ● If a declared parameter is missing or out of order no error is generated ● Functions may be declared in statement or
  • 11. Introduction to Objects