Where can be used to filter records same as Sql Where clause.

Sql (Where)

Select * From Table_Name
Where
Column1=some_value
and
Column2=some_another_value;

JsStore

connection.select({
    from: "Table_Name",
    where: {
        column1: some_value,
        column2: some_another_value
    }
}).then(function(results) {
    //results will contains no of rows deleted.
    console.log(results);
}).catch(function(error) {
    alert(error.message);
});

Example