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).
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.
Inside the function, the arguments (the parameters) behave as local variables. _____
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) You will learn a lot more about function invocation later in this tutorial.
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”: ___
Using the example above, toCelsius refers to the function object, and toCelsius() refers to the function result.
Accessing a function without () will return the function object instead of the function result.