JavaScript, JavaScript Functions, JavaScript local and Global variables
Today in this tutorial we discuss on the topic is:
JavaScript Functions:
A JavaScript function is a block of code designed to perform a particular task.
A JavaScript function is executed when “something” invokes it (calls it).
JavaScript Function Syntax
 A JavaScript function is defined with the function keyword, followed by a name, followed by parentheses ().
 Function names can contain letters, digits, underscores, and dollar signs (same rules as variables).
 The parentheses may include parameter names separated by commas: (parameter1, parameter2, …)
 The code to be executed, by the function, is placed inside curly brackets: {}
 Function parameters are listed inside the parentheses () in the function definition.
 Function arguments are the values received by the function when it is invoked.
 Inside the function, the arguments (the parameters) behave as local variables.
Function Invocation
The code inside the function will execute when “something” invokes (calls) the function:
 When an event occurs (when a user clicks a button)
 When it is invoked (called) from JavaScript code
 Automatically (self-invoked)
Function Return
When JavaScript reaches a return statement, the function will stop executing.
• If the function was invoked from a statement, JavaScript will “return” to execute the code after the invoking statement.
• Functions often compute a return value. The return value is “returned” back to the “caller”:
Why Functions:
You can reuse code: Define the code once, and use it many times.
You can use the same code many times with different arguments, to produce different results.
Local Variables:
 Variables declared within a JavaScript function, become LOCAL to the function.
 Local variables can only be accessed from within the function. Since local variables are only recognized inside their functions, variables with the same name can be used in different functions.
 Local variables are created when a function starts, and deleted when the function is completed.

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