How to select multiple nodes

How to select multiple nodes using myDiagram.select() ?

My Code is:-

myDiagram.select(myDiagram.findNodeForKey(diagram_data[i].data.key));

I want multiple nodes selected by code.

Diagram.select only selects a single Part. You want to call Diagram | GoJS API instead.

I am using the following code

var diagram_data = myDiagram.selection.toArray();
var node_arr = [];
for (i = 0; i < diagram_data.length; i++) {
node_arr.push(diagram_data[i].part);
};
myDiagram.selectCollection(node_arr);

It is not selecting.
What wrong in my code?

Your code appears equivalent to:

myDiagram.selectCollection(myDiagram.selection)

which does nothing.