Google Spreadsheets replace cell range with data minus empty cells - google-app-engine

Question

I am making a script allows you to consolidate a todo list after finished items are erased.
I am getting a range, using an if statement to push all non-zero cell values from the specified range to an array, clearing the cell range and then re-pasting the new array (minus the cells with no data) back into the same range. Here is my code: (thanks mogsdad!)
function onOpen()
{
var spreadsheet = SpreadsheetApp.getActive();
var menuItems = [
{name: 'Consolidate To-Do list', functionName: 'consolidatetodolist_'}
];
spreadsheet.addMenu('LB functions', menuItems);
};
function consolidatetodolist_()
{
var ss = SpreadsheetApp.getActiveSpreadsheet();
var sheet = ss.getSheets()[0];
var range = sheet.getRange("A2:A19");
var rangeValues = range.getValues();
var todosArray = new Array();
for (var i = 0 ; i < rangeValues.length ; i++ ) {
var row = rangeValues[i];
var cell = row [0];
if (null !== cell && "" !== cell) {
todosArray.push(row);
};
};
Logger.log(todosArray);
range.clearContent();
range.offset(0,0,todosArray.length).setValues(todosArray);
};

Answer 1

Your edit trigger should not be manipulating the menu. You should have an onOpen trigger do that. If you want the consolidation to be automatic, then you could drive THAT from your onEdit.
In your consolidatetodolist_() function, you've got a handful of errors regarding value assignment, Javascript fundamentals.
Using the SpreadsheetApp services to get the value of valueInstance isn't necessary. You've already got it, in rangeValues[i][0]. Note the two indexes; the data stored in rangeValues is a two-dimensional array, even though your range was one column. The first index is rows, the second is columns. (Opposite order from A1Notation.)
if ( range.getLength(valueInstance) !== 0 ) should crash, because range is an instance of Class Range which has no getLength() method. What you intend to check is whether the current cell is blank. Since spreadsheet data can be of three javascript types (String, Number, Date), you need a comparison that can cope with any of them, as well as an empty cell which is null. Try if (null !== cell && "" !== cell)...
When you get to setValues, you will need to supply a two-dimensional array that is the same dimensions as range. First, you need to ensure todosArray is an array of arrays (array of rows, where a row is an array of cells). Easiest way to do that here is to use var row = rangeValues[i]; var cell = row[0];, then later todosArray.push(row);. Since you are clearing the original range first, you could then define a new range relative to it using offset(0,0,todosArray.length).setValues(todosArray).
Other nitpicking:
You've got the idea of using meaningful variable names, good. But instead of valueInstance, cell would make this code clearer.
Use of "magic numbers" should be avoided, because it makes it harder to understand, maintain, and reuse code. Instead of i < 18, for example, you could use i < rangeValues .length. That way, if you modified the size of the range you're consolidating, the for loop would adapt without change.
Declaring var i outside of the for loop. No error with what you've done (although a declaration with no value assigned is bad), and it makes no difference to the machine, but for humans it's clearer to define i in the for loop, unless you need to use it outside of the loop. for (var i = 0; ...