Understanding procedures in Snowflake (javascript)

Question

I came through lately following line of code while analyzing 3rd party data script.

  CREATE OR REPLACE PROCEDURE WH.SCHEMA.PROCEDURE_NAME(DATE_OF_LOAD STRING) --input which will be binded later
  RETURNS STRING
  LANGUAGE javascript
  AS $$

   var drop_table = `drop table if exists TABLE_NAME;`; 
   var stmt_drop_table = snowflake.createStatement( {sqlText: drop_table} );
   var incremental_data =
     `CREATE TABLE AS <many arguments>

      WHERE P.CZAS_MODYF_SF >= :1 --this is where biding of DATE_OF_LOAD occurs)

   SELECT *, HASH(*) HASH FROM (
                             SELECT <arguments>
                            FROM CTE) q; `;

   var stmt_incremental_data = snowflake.createStatement( {sqlText: incremental_data,binds: [DATE_OF_LOAD ].map(function(x){return x === undefined ? null : x}) } );

   try {

    stmt_drop_table.execute();  
    stmt_incremental_data.execute(); 
    rtr = "Success!";
    return rtr;
    }

   catch (err) {

       return "Failed: " + err;
}  
$$
;

Entire challenge I have is with:

var stmt_incremental_data = snowflake.createStatement( {sqlText: incremental_data,binds: [DATE_OF_LOAD ].map(function(x){return x === undefined ? null : x}) } ).

object.method part is clear. Same for binds. Code after binds is my issue here.

Another topic: Snowflake interpretes method's parameters as a JSON. Does it mean that bind value can be extended by assigning JS code? I'll be greatly thankful for help and explanation.

Answer 1

The reason I did not post this as an answer initially is that JavaScript is not my area of expertise. I did dabble in it for a few months.

But in order to understand what is going on with:

[DATE_OF_LOAD ].map(function(x){return x === undefined ? null : x})

You need to break it down:

 x === undefined ? null : x

This is called an elvis operator and is the equivalent of :

if (x === undefined) 
{ 
  return null
} else { 
  return x 
} 

Now that we know what the function does, we need to understand the map method. But in short it creates a new array with the results of calling a provided function on every element in the calling array.

So the simple answer copied from my comment is: if DATE_OF_LOAD is undefined it will replace it with null, otherwise it will use whatever value is stored in DATE_OF_LOAD. That is because SQL does not know how to handle undefined. But here is the reasoning for my answer.