Check boxes are stand-alone elements; that is, they don't
interact with neighboring elements like radio buttons do. Therefore they
are a bit easier to use. Using JavaScript you can test if a check box is
checked or not using the checked property. Likewise, you can set the
checked property to add or remove the checkmark from a check box.
<SCRIPT>
function calculate(form,
callingField) {
if (callingField == "result") { //
is the calling field the "result" field?
//
is the "square" check box checked?
if (form.square.checked)
form.entry.value = Math.sqrt(form.result.value);
else form.entry.value
= form.result.value / 2;
}
else {
if (form.square.checked)
form.result.value = form.entry.value * form.entry.value;
// if (form.square.checked)
form.result.value = Math.pow(form.entry.value,
2)
else form.result.value = form.entry.value * 2;
}
}
</SCRIPT>
<FORM>
Value:
<INPUT
TYPE="text"
NAME="entry"
VALUE="0"
onChange="calculate(this.form,
this.name);">
Action: (default double/half)
<INPUT
TYPE="checkbox"
NAME="square"
onClick="calculate(this.form,
this.name);">
Square/Square Root Result:
<INPUT
TYPE="text"
NAME="result"
VALUE="0"
onChange="calculate(this.form,
this.name);">
</FORM>
calculate(this.form,
this.name) passes 2 parameters:
this.form -- because we want to
pass all the form's information to the function
this.name -- to tell the function
what particular form element made the call
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