The following code example from the SDK shows how to set values in a field of type Lookup.
//Create an array to set as the DataValue for the lookup control.
var lookupData = new Array();
//Create an Object add to the array.
var lookupItem= new Object();
//Set the id, typename, and name properties to the object.
lookupItem.id = '{1AAC1363-01A1-DB11-8432-0003FF9CE217}';
lookupItem.typename = 'account';
lookupItem.name = 'A Bike Store';
// Add the object to the array.
lookupData[0] = lookupItem;
// Set the value of the lookup field to the value of the array.
crmForm.all.parentaccountid.DataValue = lookupData;
Things to note above are that we create an array instance and the an object instance. The Javascript language provides a short hand way of creating instances of these classes.
The Object shorthand allows us to replace the lookupItem variable (defined in lines 4 to 8 above) with the following:
{id:'{1AAC1363-01A1-DB11-8432-0003FF9CE217}',
typename:'account',
name:'A Bike Store'}
We can create an array instance by using square brackets [] so lookupData (defined in lines 2 and 10) could become:
[lookupItem]
Putting all together we can remove both the variables in the example and use the following instead:
crmForm.all.parentaccountid.DataValue = [{
id:'{1AAC1363-01A1-DB11-8432-0003FF9CE217}',
typename:'account',
name:'A Bike Store'}];
In conclusion the shorthand makes a lot cleaner code once you understand the JavaScript shorthand notation
