Page 139 - CITS - Computer Software Application -TT

COMPUTER SOFTWARE APPLICATION - CITS

Why Functions?

With functions you can reuse code
You can write code that can be used many times.
You can use the same code with different arguments, to produce different results.
The () Operator
The () operator invokes (calls) the function:
Example

Convert Fahrenheit to Celsius:
function to Celsius (fahrenheit) {
return (5/9) * (fahrenheit-32);
}

let value = to Celsius(77);
Accessing a function with incorrect parameters can return an incorrect answer:
Example
function to Celsius (fahrenheit) {
return (5/9) * (fahrenheit-32);

}
let value = to Celsius();
Accessing a function without () returns the function and not the function result:
Example

function to Celsius (fahrenheit) {
return (5/9) * (fahrenheit-32);
}
let value = to Celsius;
Note
As you see from the examples above, toCelsius refers to the function object, and toCelsius() refers to the function
result.
Functions Used as Variable Values
Functions can be used the same way as you use variables, in all types of formulas, assignments, and calculations.

Example
Instead of using a variable to store the return value of a function:
let x = to Celsius(77);
let text = “The temperature is “ + x + “ Celsius”;

You can use the function directly, as a variable value:
let text = “The temperature is “ + to Celsius(77) + “ Celsius”;
Local Variables
Variables declared within a JavaScript function, become LOCAL to the function.
Local variables can only be accessed from within the function.
Example

// code here can NOT use carName

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CITS : IT&ITES - Computer Software Application - Lesson 37 - 46