Alert prompt is a file is missing when trying to import

[threedeeNYC]

My script works to replace a file in my bin. 
I highlight multiple AVItems in my bin, get the naming convention, and replace them with new files from a specified directory. Works, all good.

My issue now is i want an alert if the file im trying to import is not in the directory.

so in my code i have this snippet. I think my idea for doing the if statment if its ===undefined is not right.

// these two vars i got from the highlighted items in my bin.
var mFinalFile = myPath + myRepFile + zeroAdd +myFormat;   
                            var mFileName = myRepFile + zeroAdd + myFormat;
                            
                            //establish my new import file
                            var myImport = new File(mFinalFile);
                            
                            //if the file isnt in the location...
                            if (myImport === undefined){
                                //give an alert
                                alert("Error: " + mFileName + " missing from this lcoation.");
                                }else{                            
                                    //make it a seqence
                                    myImport.sequence = true;                                    
                                    //replace current selected item with the file created from the above process. The "false" is not forcing alphabetical.
                                    item.replaceWithSequence(myImport, false);     
                                    }

[threedeeNYC]

I always figure it out 4 seconds after i ask. I needed to use the isValid().

if (isValid(myImport) === false){
                                //give an alert
                                alert("Ya done messed up! \r Error: " + mFileName + " missing.");
                                }else{                            
                                    //make it a seqence
                                    myImport.sequence = true;                                    
                                    //replace current selected item with the file file created from the above process. The "false" is not forcing alphabetical.
                                    item.replaceWithSequence(myImport, false);     
                                    }

[threedeeNYC]

Dammit! no that wasnt it. Close

[Paul Tuersley · Accepted solution]

if (myImport.exists == false)

which can equally be written as:

if (!myImport.exists) 

[threedeeNYC]

thank you. I searched for .exists on:
https://ae-scripting.docsforadobe.dev/

And it came up empty.

[Paul Tuersley]

The After Effects scripting guide doesn't include stuff that is common to all Extendscript apps such as file system and UI. You can find that here:

https://extendscript.docsforadobe.dev/file-system-access/file-object.html#file-object-properties