[Solved] What does this code mean? JavaScript [closed]

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dataStuff.forEach(function (a) {
    grouped[a.Tag] = grouped[a.Tag] || []; //if  grouped[a.Tag] array is undefined make it an array
    grouped[a.Tag].push(a);                //try to push into array.
});

Explaining your code.

The line

grouped[a.Tag].push(a); is supposed to push a values into the array grouped[a.Tag]. If at all this grouped[a.Tag] array is undefined you will get a error saying grouped[a.Tag] is undefined. So to overcome this problem this line

grouped[a.Tag] = grouped[a.Tag] || []; is used.

Here grouped[a.Tag] || [] if at all grouped[a.Tag] is undefined your above line will be equivalent to

grouped[a.Tag] = []; That is create a new array.

Else if grouped[a.Tag] is defined then you don’t have to do anything so just assign it to itself.

So the idea is if grouped[a.Tag] is undefined then create a new array else do nothing as you are good to go.

solved What does this code mean? JavaScript [closed]