You can use the following code to retrieve list item by id
CODE
- JSOM Query List Items
- JSOM Retrieve all list fields
- JSOM Get ListItem By Id
- JSOM Query with search web services
- JSOM Retrieve all lists
- JSOM Update List Items
- JSOM Delete List Items
- JSOM Create List Items
- JSOM Get group members
- JSOM Get files from a folder
- JSOM Get current user detail
- JSOM Get list content types
- JSOM Initiate SharePoint workflow
- JSOM Set Item Level Permission
- JSOM Get current user groups
- JSOM Get Tasks From Workflow Instance
- JSOM SharePoint Open Dialog Feature
- JSOM Approve / Reject Task
- JSOM Add / Remove users from / to user groups
- JSOM People Picker Control
- JSOM Create / Delete group