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Accessing form fields

Every form field, whether it is a button, text box, or other, is contained in the form’s

elements

collec-

tion. You can access the various fields in the collection by using their

name

attributes or their positions

in the collection:

var oFirstField = oForm.elements[0]; //get the first form field

var oTextbox1 = oForm.elements[“textbox1”];//get the field with the name “textbox1”

In the shorthand version for accessing an element by its name, every form field becomes a property of

the form itself and can be accessed directly by using its

name

var oTextbox1 = oForm.textbox1; //get the field with the name “textbox1”

If the name has a space in it, use bracket notation instead:

var oTextbox1 = oForm[“text box 1”]; //get the field with the name “text box 1”

Form field commonalities

All form fields (except for hidden fields) contain common properties, methods, and events:

The

disabled

property is used both to indicate whether the control is disabled as well as to

actually disable the control (a disabled control doesn’t allow any user input, but gives no visual

indication that the control is disabled).

The

form

property is a pointer back to the form of which the field is a part.

The

blur()

method causes the form field to lose focus (by shifting the focus elsewhere).

The

focus()

method causes the form field to gain focus (the control is selected for keyboard

interaction).

The

blur

event occurs when the field loses focus; the

onblur

event handler is then executed.

The

focus

event occurs when the field gains focus; the

onfocus

event handler is then executed.

For example:

var oField1 = oForm.elements[0];

var oField2 = oForm.elements[1];

//set the first field to be disabled

oField1.disabled = true;

//set the focus to the second field

oField2.focus();

Of course, you can still use

document.getElementById()

with a form field’s ID to

retrieve it directly. The methods discussed in this section are most useful when you

need to iterate over all the fields in a single form.

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