APEX

Hello,
How can I add the values within a Grid
I did the following
var model = apex.region("IG1").widget().interactiveGrid("getViews","grid").model;
var var1 = model.getFieldKey("VAR1");
var sum;
model.forEach(function(igrow) {
sum = Number(sum) + Number(igrow[var1]);
console.log("VAR1" + var1);
console.log(Number(igrow[var1]));
console.log(sum);
})
console.log("Wert");
console.log(sum);

But it is always like this and not a sum

Thanks