In this article you will see how to get the lookup field value for a list item in SharePoint 2010 using ECMAScript. I have a custom list named "Custom" which has a lookup column named "LookupSingleValue".
And I have the following item in the list as shown in the following figure.
1. Navigate to the SharePoint site (I have a site page created in my site where I am going to add the content editor web part).
2. Go to Site Actions, click on Edit Page.