Unknown array notation javascript

Question

I've come across the following code, I'm having trouble getting my head around it.

selCOption2[i, 'labelname'] = selOption2Arr[i];

a larger excerpt

var selCOption2 = [];
 var stringContent = '';
 jQuery('#txtTypes').attr("value", selOption1);
 for(var i=0; i<selOption2Arr.length; i++) {
 if(selOption2Arr[i] != 'Plain' || selOption2Arr[i] != 'plain') {
 selCOption2[i, 'labelname'] = selOption2Arr[i];
 selCOption2[i, 'keyname'] = keyname+"_"+selOption2Arr[i].toLowerCase()+"_"+selOption3Arr[0].toLowerCase();
 for(var ifm = 0; ifm < proJsonDetails.images.length; ifm++) { 
 if(proJsonDetails.images[ifm].indexOf(selCOption2[i, 'keyname']) > 0) {
 selCOption2[i, 'image'] = proJsonDetails.images[ifm];
 }
 }
 }
 }

• Rhumborl: selCOption2[i]['labelname'] = selOption2Arr[i];
• apsillers: This is valid syntax, but not a sensible thing to do. The expression "i, 'labelname'" is a comma operator expression, and the effect is no different from selCOption2['labelname'] = ... (except for the highly unusual case where there might be a getter function on i, which is not the case here).
• The Paramagnetic Croissant: ...and so what you have is equivalent with selCOption2['labelname'] = selOption2Arr[i];.

Answer 1

See a reduced test case:

var a = [ 'x', 'y', 'z' ];
var o = {};
var i = 1;
o[i, 'labelname'] = a[i];
console.log(o);

which gives:

{ labelname: 'y' }

The , operator evaluates as whatever is on the right hand side of it.

There doesn't appear to be any point in having i, in that code.