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Can't you create a lookup in your list2 to the list1 and make it required? That way the users have to choose an existing code.<br />
<br />
if you still need to do this, yes you can use javascript to make a call to the list (webservices if using 2007) &nbsp;by using the client obejct model (if using &nbsp;2010)
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Can't you create a lookup in your list2 to the list1 and make it required? That way the users have to choose an existing code.

if you still need to do this, yes you can use javascript to make a call to the list (webservices if using 2007)  by using the client obejct model (if using  2010)

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Was hoping for a javascript that might work
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Was hoping for a javascript that might work

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Look at SPservices on codeplex...its the javascript swiss army knife for SharePoint
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Look at SPservices on codeplex...its the javascript swiss army knife for SharePoint

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I don't see anything specifically called SPservices on codeplex, do you mean JQuery?
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I don't see anything specifically called SPservices on codeplex, do you mean JQuery?

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I have a couple custom lists, lets call them list1 and list2<br />
<br />
lets say that list1 is a list of codes that is updated daily from an extyernal source.<br />
<br />
code1<br />
code2<br />
code3<br />
code4<br />
<br />
list2 is my working list where we enter information, the first value entered in a field called code and I would like to have something kick off when that first field is entered and you mouse out of the field that checks list1 to see if the code exists. &nbsp;If it doesnt it should come back and say invalid code and not allow the screen to be entered.<br />
<br />
can this be done??
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I have a couple custom lists, lets call them list1 and list2

lets say that list1 is a list of codes that is updated daily from an extyernal source.

code1
code2
code3
code4

list2 is my working list where we enter information, the first value entered in a field called code and I would like to have something kick off when that first field is entered and you mouse out of the field that checks list1 to see if the code exists.  If it doesnt it should come back and say invalid code and not allow the screen to be entered.

can this be done??

Need a SharePoint List Trick

Microsoft Sharepoint is a software platform and family of software products used for collaboration and web publishing combined. These capabilities include developing web sites, portals, intranets, content management systems, search engines, wikis, blogs, and other tools for business intelligence and collaboration. SharePoint has a Microsoft Office-like interface, and it is closely integrated with the Office suite.

Microsoft SharePoint

JavaScript is a dynamic, object-based language commonly used for client-side scripting in web browsers. Recently, server side JavaScript frameworks have also emerged. JavaScript runs on nearly every operating system and  in almost every mainstream web browser.