Using Javascript to Manipulate a List Form Field

When might you use this?

It’s pretty easy to set a field’s default value through the list settings in the browser UI, so why might you need Javascript to set a default field value? The reason is that field default values can only take static values or simple formulae based on the current user or today’s date. If that meets your needs, then I’d definitely recommend sticking with that method. Sometimes, though, you may want the form to fill with default values based on the user’s interaction with the previous page, and that’s exactly where this method comes in.

How does it work?

In short, we add some Javascript to the page that runs when the body is loaded. This Javascript parses the page’s query string, locates the HTML objects that are rendered by the relevant SharePoint fields, and sets their value based on the information in the query string.

getTagFromIdentifierAndTitle

The most important part of our solution is the “getTagFromIdentifier” function. This function finds the HTML element rendered by a given SharePoint FormField control. It takes the following parameters:

• tagName – The name of the tag rendered in the form’s HTML
• identifier – The string associated with the SharePoint type of the relevant field
• title – The value of the relevant HTML tag’s “title” attribute, which also matches the field’s display name

Here’s a partial table of SharePoint column types and their corresponding “identifiers” and “tagNames”:

SharePoint Field Type	identifier	tagName
Single Line of Text	TextField	input
Multiple Lines of Text	TextField	input
Number	TextField	input
Currency	TextField	input
Choice (dropdown)	DropDownChoice	select
Lookup (single)*	Lookup	select
Lookup (multiple)	SelectCandidate; SelectResult	select
Yes/No	BooleanField	input

*Lookups are a bit more complicated because Lookup FormFields render differently when the target list contains more than 20 items. See the end of the post for an example.

function getTagFromIdentifierAndTitle(tagName, identifier, title) {

var len = identifier.length;

var tags = document.getElementsByTagName(tagName);

for (var i=0; i < tags.length; i++) {

var tempString = tags[i].id;

if (tags[i].title == title && (identifier == "" || tempString.indexOf(identifier) == tempString.length - len)) {

return tags[i];

}

}

return null;

}

fillDefaultValues

Now that we have the HTML elements that we want to set, we need the values with which to set them. In our solution, we wrote the “fillDefaultValues” function, which parses the page’s querystring and then uses the values to set the field defaults.

function fillDefaultValues() {

var qs = location.search.substring(1, location.search.length);

var args = qs.split("&");

var vals = new Object();

for (var i=0; i < args.length; i++) {

var nameVal = args[i].split("=");

var temp = unescape(nameVal[1]).split('+');

nameVal[1] = temp.join(' ');

vals[nameVal[0]] = nameVal[1];

}

// Set HTML element default values here

}

_spBodyOnLoadFunctionNames

In most cases SharePoint pages are based on a master page that contains the “body” element. These content pages can’t directly add a function to the body’s onload event. In order to work around this limitation, SharePoint provides the “_spBodyOnLoadFunctionNames” array. When the body is loaded, the onload event handler executes each function whose name is contained in this array. We added “fillDefaultValues” to the array so that it would run when the body’s onload event fires.

_spBodyOnLoadFunctionNames.push("fillDefaultValues");

All Together Now

With the script above, you can set most different field types to any value from the querystring – or any other source that javascript can access. Below is a full example of the script we use to set the default value of a Lookup field based on an ID stored in the querystring. You’ll notice that setting a Lookup field is a bit more complicated than some other field types. The reason is that Lookup FormFields are rendered with different HTML when the target list contains more than 20 items.

Enjoy!

<script type="text/javascript">

// This javascript sets the default value of a lookup field identified

// by <<FIELD DISPLAY NAME>> to the value stored in the querysting variable

// identified by <<QUERYSTRING VARIABLE NAME>>

// Customize this javascript by replacing <<FIELD DISPLAY NAME>> and

// <<QUERYSTRING VARIABLE NAME>> with appropriate values.

// Then just paste it into NewForm.aspx inside PlaceHolderMain

_spBodyOnLoadFunctionNames.push("fillDefaultValues");

function fillDefaultValues() {

var qs = location.search.substring(1, location.search.length);

var args = qs.split("&");

var vals = new Object();

for (var i=0; i < args.length; i++) {

var nameVal = args[i].split("=");

var temp = unescape(nameVal[1]).split('+');

nameVal[1] = temp.join(' ');

vals[nameVal[0]] = nameVal[1];

}

setLookupFromFieldName("<<FIELD DISPLAY NAME>>", vals["<<QUERYSTRING VARIABLE NAME>>"]);

}

function setLookupFromFieldName(fieldName, value) {

if (value == undefined) return;

var theSelect = getTagFromIdentifierAndTitle("select","Lookup",fieldName);

// if theSelect is null, it means that the target list has more than

// 20 items, and the Lookup is being rendered with an input element

if (theSelect == null) {

var theInput = getTagFromIdentifierAndTitle("input","",fieldName);

ShowDropdown(theInput.id); //this function is provided by SharePoint

var opt=document.getElementById(theInput.opt);

setSelectedOption(opt, value);

OptLoseFocus(opt); //this function is provided by SharePoint

} else {

setSelectedOption(theSelect, value);

}

}

function setSelectedOption(select, value) {

var opts = select.options;

var l = opts.length;

if (select == null) return;

for (var i=0; i < l; i++) {

if (opts[i].value == value) {

select.selectedIndex = i;

return true;

}

}

return false;

}

function getTagFromIdentifierAndTitle(tagName, identifier, title) {

var len = identifier.length;

var tags = document.getElementsByTagName(tagName);

for (var i=0; i < tags.length; i++) {

var tempString = tags[i].id;

if (tags[i].title == title && (identifier == "" || tempString.indexOf(identifier) == tempString.length - len)) {

return tags[i];

}

}

return null;

}

</script>

source :http://blogs.msdn.com/sharepointdesigner/archive/2007/06/13/using-javascript-to-manipulate-a-list-form-field.aspx