wbcreateclaim

api.get({
  action:'query',
  continue:'',
  meta:'tokens',
  format:'json'
}).done(function(token) {
  api.post({
    action: 'wbcreateclaim',
    entity: 'Q4115189',
    property: 'P901',
    snaktype: 'value',
    token: token.query.tokens.csrftoken,
    value: '{"entity-type":"item","numeric-id":1}' // String now
  }).done(function(data) {
    console.log(data);
  });
});

/*
Error message

{
    "servedby": "mw1231",
    "error": {
        "code": "invalid-snak",
        "info": "Invalid snak (Can only construct StringValue from strings)",
        "messages": [
            {
                "name": "wikibase-api-invalid-snak",
                "parameters": [],
                "html": {
                    "*": "Invalid snak"
                }
            }
        ],
        "*": "See https://www.wikidata.org/w/api.php for API usage"
    }
}
*/