To open a regular share dialog like this one:
I use this following code:
FB.ui({
method: 'share',
href: 'https://www.happymood.co',
}, function(response){});
Now if I want the default option to show "On your Friends' Timeline" instead of "On your own Timeline", what changes must I make to this code?
It´s not possible at all to define another default setting. You can check out the Facebook docs to see what parameters you can use: https://developers.facebook.com/docs/sharing/reference/share-dialog