Functions are "self contained" modules of code that accomplish a specific task. Functions usually "take in" data, process it, and "return" a result. Once a function is written, it can be used over and over and over again.
JavaScript provides functions similar to most of the scripting and programming languages.
In JavaScript, a function allows you to define a block of code, give it a name and then execute it as many times as you want.
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: {}
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The code inside a function is not executed when the function is defined.
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The code inside a function is executed when the function is invoked.
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It is common to use the term "call a function" instead of "invoke a function".
