Chapter 5

[Christopher Bergin]

I'm wondering why variables that are declared at the beginning of a function are assigned the form elements and not their corresponding values. For instance...

 

// Get a reference to the form elements:

 

var type = document.getElementById('type');

var years = document.getElementById('years');

 

the program would then go on to check conditions...

 

 

// Convert the year to a number:

if (years && years.value) {

years = parseInt(years.value, 10);

}

 

// Check for valid data:

if (type && type.value && years && (years > 0) )

 

would the following revision be as efficacious?

 

 

var type = document.getElementById('type').value;

var years = document.getElementById('years').value;

 

 

 

Chris

[HartleySan]

Your suggestion is not wrong, but also not recommended. By assigning a reference to a DOM element to a variable, you can first test whether the DOM element exists at all, which is a good idea.

 

For example, if an element with the ID "years" does not exist, then trying to assign the value of such an element immediately to a variable will cause an error.

 

Also, it never hurts to assign a DOM reference to a variable, as you never know if you'll need the DOM reference again (and searching through the DOM twice for the same element is a waste).

[Christopher Bergin]

duly noted. Thanks for the response HartleySan.

 

Chris