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Set FORM field value based on value of another field

Posted on 2001-08-28
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Last Modified: 2012-05-04
Here's what I need:

A small javascrip application, as horizontally-compatible as possible (with any details of browsers/situations where it may not be compatible and why) that will set the value of one field in a FORM based on the value of another field.  And a variation that can set the value of one field to equal the value of another field plus some additional text.

I want to know all the ways this script can be executed, i.e. do I have to put a reference in the FORM or submit button or is there a way to have it function automatically by embedding the script at different points in the html page?

Example:

<form method="post" action="...">
<select name="fieldA">
<option value="a">First Option
<option value="2">Second Option
..
</select>
... (more stuff)

I'd like examples of ways a hidden field, say like:
<input type="hidden" name="fieldAdesc" value="..">

can be set to:
  "First Option" if fieldA="a"
  "Second Option" if fieldA="2"
  etc.

and how in which this can be done... only upon submit, in real time to change the field value at the time of selecting the pulldown - etc?  Ideally, it would be nice to have the script set the field value when the pulldown is selected - and can this be done without changing the FORM or SUBMIT references?

Thanks in advance for your assistance.  Extra good kharma will also be awarded to the person with the most complete answer!
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Question by:maabu
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Accepted Solution

by:
de_britto earned 50 total points
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<Script language="JavaScript">
fnSetCombo() {
document.fm.fieldAdesc.value = document.fm.fieldA.options[document.fm.fieldA.selectedIndex].text;
}
</Script>


Call this function 'onChange' of select control
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Expert Comment

by:Michel Plungjan
Comment Utility
Or neater (adding a "function" too) :

<Script language="JavaScript">
function fnSetCombo(theSel) {
theSel.form.fieldAdesc.value = theSel.options[theSel.selectedIndex].text;
}
</Script>

<select name="fieldA" onChange="fnSetCombo(this)">

or all in the onChange - no need for script tags:

<select name="fieldA"
onChange="this.form.fieldAdesc.value=this.options[this.selectedIndex].text">
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Author Comment

by:maabu
Comment Utility
I know nothing of Javascript so "dummy-fy" this for me by showing me how this would fit into the sample form if you fine gentlemen wouldn't mind.   I can't tell what phrases are variables and what are reserved words either.. can you make the distinction?

Thanx
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Expert Comment

by:Michel Plungjan
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<form method="post" action="...">

<select name="fieldA"
onChange="this.form.fieldAdesc.value=this.options[this.selectedIndex].text">

<option value="a">First Option
<option value="2">Second Option
</select>
<input type="hidden" name="fieldAdesc" value="">

Each field has a "form"
that points at the form it is in
so this.form
is the select's form
this.form.fieldAdesc
is the hidden field as seen from the select
the select has options: this.options
they are accessed via the selectedIndex e.g. 0 for the first option, 1 for the second (javascript counts from 0)

the notation
this.options[this.selectedIndex]
is the selected option.

It has a .value and a .texts, the latter being what you asked for

It is trigger when the user changes the select e.g. onChange
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LVL 75

Expert Comment

by:Michel Plungjan
Comment Utility
Oops - typo:
It has a .value and a .texts,
should be
It has a .value and a .text,

Michel
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Expert Comment

by:ahosang
Comment Utility
No comment has been added lately, so it's time to clean up this TA.
I will leave a recommendation in the Cleanup topic area that this question is:
points to mplungjan
Please leave any comments here within the next seven days.
 
PLEASE DO NOT ACCEPT THIS COMMENT AS AN ANSWER!
 
ahosang
EE Cleanup Volunteer
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Expert Comment

by:Michel Plungjan
Comment Utility
points to me or split me and deBritto
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Expert Comment

by:SpideyMod
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Points split

SpideyMod
Community Support Moderator @Experts Exchange

mplungjan points for you at:
http://www.experts-exchange.com/Web/Web_Languages/JavaScript/Q_20526348.html
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