Question

I want to create a JSON hierarchy structure of unknown objects, so it must be handled recursively.

Here’s my function, where angular.element.isEmptyObject() is inherited from jQuery, and angular.copy() is a function that creates a deep copy of the object (I’m using AngularJS).

function recurseTree(tree, newKey, newId) {
    if(angular.element.isEmptyObject(tree)) {
        tree[newKey] = {_id: newId};
    } else {
        for(var key in tree) {
            if(typeof tree[key] == 'object') recurseTree(tree[key], newKey, newId);
            else tree[newKey] = {_id: newId};
        }
    }
    return angular.copy(tree);
}

Now run this:

var testT = {};
console.log(recurseTree(testT, 'a', '1'));
console.log(recurseTree(testT, 'b', '2'));
console.log(recurseTree(testT, 'c', '3'));
console.log(recurseTree(testT, 'd', '4'));
console.log(recurseTree(testT, 'e', '5'));

You’ll notice that the first and second ones return as expected:

{ 
    a: { 
        _id: '1',
        b: {
            _id: '2'
        }
    }
}

but the third one is where I run into trouble.

{ 
    a: { 
        _id: '1',
        b: {
            _id: '2',
            c: {
                _id: '3'
            }
        },
        c: {
            _id: '3'
        }
    }
}

What do I need to fix to get the c object appended ONLY as a child of b, rather than also as a child of a? I’m stumped.

Here’s a JSFiddle of it in action, check your console for the results. http://jsfiddle.net/winduptoy/Mjq5D/2/

Answer 1

Try this:

function recurseTree(tree, newKey, newId) {
    if(angular.element.isEmptyObject(tree)) {
        tree[newKey] = {_id: newId};
        return;
    } 

    var child = null; // find current tree's child
    for(var key in tree) {
        if (key != '_id') {
            child = tree[key]; // found a child
            break;
        }
    }
    if (child) { // recursively process on child
        recurseTree(child, newKey, newId);
    } else { // no child, so just fill the tree
        tree[newKey] = {_id: newId};
    }
}

Test:

var testT = {};
recurseTree(testT, 'a', '1');
console.log(testT);  
recurseTree(testT, 'b', '1');
console.log(testT); 
recurseTree(testT, 'c', '1');
console.log(testT); 
recurseTree(testT, 'd', '1');
console.log(testT); 
recurseTree(testT, 'e', '1');
console.log(testT);

Please be noted that I have not used angular.copy(tree) for the performance’s sake.
If you don’t want to change the tree, copy it before passing it to the function recurseTree. Please try it on jsFiddle.