array of custom object in javascript - eliminate empty occurrence

Question

I have a custom object that I would like to create an array of. When creating my array it creates an occurrence with empty properties, I understand why, but I would like to avoid this. I realize I could just delete the occurrence with the empty properties, but is there a better way?

function FileToPassBack(path, originalFileName, modifiedDate, newFilename) {
    if (!(this instanceof FileToPassBack)) {
        return new FileToPassBack(namepath, originalFileName, modifiedDate, newFilename);
    }
    this.Path = path;
    this.OriginalFileName = originalFileName;
    this.ModifiedDate = modifiedDate;
    this.NewFileName = newFilename;
}

function PostSelectedItems() {
    var allFilesToPassBack = new Array(new FileToPassBack());

     $('#fileNamesTable').find('tbody>tr:visible')
                         .each(function (index, element) {
                                var row = $(this);
                                if (row.find('input[type="checkbox"]').is(':checked'))
                                {
                                    var path = row.find('.pathTDClass').html();
                                    var originalFileName = row.find('.originalFileNameTDClass').html();
                                    var modifiedDate = row.find('.modifiedDateTDClass').html();
                                    var newFileName = row.find('input[class="newFileNameTDClass"]').val();

                                    var currentFileToAdd = new FileToPassBack(path, originalFileName, modifiedDate, newFileName)
                                    allFilesToPassBack.push(currentFileToAdd);
                                }
                            });

    //post path, original file name, modified date, new file name
    var objectAsJSON = JSON.stringify(allFilesToPassBack);
}

I am new to JS, so excuse me if I am way off track.

Answer 1

new Array(number)

Creating a new array with a number will initialize it with a certain number of empty elements:

var a = new Array(5);
// a = ['','','','',''];

thus when you push it will add a new entry

a.push("a");
// a = ['','','','','', 'a'];

The best practice is not to use new Array, instead use [] syntax as it is more performant.

var allFilesToPassBack = [];

JSON Stringify

although it works, you need to be aware that you are stringify-ing an array not a JSON in your example code.

Update

why [] is more performant than new Array() and considered a best practice.

When you create an array using

var a = [];

You're telling the interpreter to create a new runtime array. No extra processing necessary at all. Done.

If you use:

var a = new Array();

You're telling the interpreter, I want to call the constructor "Array" and generate an object. It then looks up through your execution context to find the constructor to call, and calls it, creating your array.

why its a best practice?

The new Array() doesn't add anything new compared to the literal syntax, it only wraps the array with an object wrapper that is not needed, only adding overhead of calling the Array constructor and creating an object wrapper around the array.

additionally defining a function Array() {} in the code, new Array() will start creating new instances from this function instead of creating an array, its an edge case, but if you need an array, just declare it with [].

You never need to use new Object() in JavaScript. Use the object literal {} instead. Similarly, don’t use new Array(), use the array literal [] instead. Arrays in JavaScript work nothing like the arrays in Java, and use of the Java-like syntax will confuse you.

Do not use new Number, new String, or new Boolean. These forms produce unnecessary object wrappers. Just use simple literals instead.

http://yuiblog.com/blog/2006/11/13/javascript-we-hardly-new-ya/

There are ton of sources, but i'll keep it minimal for this update. new was introduced to the language as it is "familiar" to other languages, as a prototypal language, the new syntax is useless and wrong, instead the language should have Object.create. but thats a different topic, you can read more about it from experts like Kyle Simpson or Douglas Crockford.

Answer 2

I think, though am unsure what your actual problem is, that you are calling var allFilesToPassBack = new Array(new FileToPassBack()); to initialize your array? You don't need to do that.

Try replacing that line with this instead.

var allFilesToPassBack = []

That will init an empty array than you can then pushto in your jquery each loop.