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

1. JavaScript
Introduction to
Functions
Charles Russell
Bennu Bird Media

2. What is a function.
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As Defined by W3Schools A function is a block of
code that will be executed when "someone" calls
it.
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Saved for later and use on demand

3. Function invocations
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functionName( parameterList);
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Parameters, or arguments, are the values to be
used by the function
– Parameters may be expressions, variables,
literals, or objects
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Ex: alert('Hello World');
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Functions may return values
– name = fullName('Charles', 'Russell');

4. Making Your Own
Functions
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Functions can be constructed two ways
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Statement form
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Expression form

5. Statement form
function nameOfFunction(parameter1, parameter2, ...) {
//statments and expressions
return result; //Optional if no value to be returned
}
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The return statement is optional and may or may not return a value
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Immediate invocation optional with () following end of code block
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If a parameter is declared and not passed no error is generated until an
attempt is made to use the missing parameter.
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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
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In this Language variables default to global
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This means that any function anywhere can use and
overwrite your values at any time
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The var keyword is what is used to limit scope to
the function in which the variable was delcare
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There is no block scope only function scope
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This means that any local variable declared in a
function can be accessed from anywhere in the
function even sub functions
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Variables in parameters have local scope

9. this Keyword
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The keyword this is a special object that refers to
different important objects based upon context.
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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
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When function used as a constructor this refers to
current instance of current function
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When as a method this refers to calling object
(normally the parent)

10. Summary
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Function are code ment to be used later
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A function is called by using its name and opening
and closing parents surround 0 or more
parameters
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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