Hi Gowtham89,
You can use following js code into lookup field onChange event in form properties.
function getLookupName(executionContext) {
var formContext = executionContext.getFormContext();
var lookupFieldObject = formContext.getAttribute("new_existingclient");
if (lookupFieldObject.getValue() != null) {
var entityName = lookupFieldObject.getValue()[0].name;
}
var company = formContext.getAttribute("new_company");
company.setValue(entityName);
}
Go Settings > Customizations > Customize the system > Web Resources to add new js resource.
Then expand Entities to open one form of the entity you need
Click 'Form Properties' to open dialog to add resource you just created.
Save and Publish all customizations.
Test:
Changing lookup field value without clicking save button, company field has been populated with lookup field name.
