Required library edition:
Required library file: dhtmlxlayout.js

returns cell's index

var ind = dhxLayout.cells("a").getIndex(); // will return 0; "a" is item's id
  // or
var inds = new Array();
dhxLayout.forEachItem(function(item){
  inds[inds.length] = item.getIndex();
});
  // inds will contain [0,1,2...] depending on pattern