The Book of JavaScript, 2nd Edition

JavaScript's Built-In Arrays

When a web browser reads an HTML page, it automatically creates a number of arrays. In the previous chapter we saw that JavaScript creates an array for each set of radio buttons with the same name. If you create a set of radio buttons named age inside a form named the_form, you can refer to the first radio button in the set like this:

window.document.the_form.age[0]

JavaScript also creates an array for the options in each pull-down menu and scrollable list. Here's how you could access the second option in a pull-down menu named gender:

window.document.the_form.gender.options[1]

These are just two of JavaScript's automatically created arrays. Browsers also automatically create an array of all the image objects on a web ...