Dynamic Object Traversing with NodeJS

Question

I have a storage object that has an object datastore in it, like so:

data = {
    name1: 'value1',
    name2: 'value2',
    child: {
        name3: 'value3',
        name4: 'value4'
    }
}

What I need to do is pass the data variable, a name, and value, and have the object update, like so:

update(data, 'name1', 'foobar');

This works fine, but here's the catch: I need to be able to send a dot-notation name and have it update the proper child attribute. For instance:

update(data, 'child.name3', 'foobar');

Here is the code I'm using to do the traversal:

function update(data, fieldName, value) {
    var field = data
    var fieldNameParts = fieldName.split('.');
    while (fieldNameParts.length)
        field = field[fieldNameParts.shift()];
    field = (value === undefined) ? null : value;
}

So the problem is that "field" contains the new value, but "data.child.name3" does not. How do I traverse and update the main data object?

Any ideas on how to solve this?

have you considered using lodash.set?

vincent
– vincent

2020-10-24 12:55:15 +00:00
Commented Oct 24, 2020 at 12:55 — vincent
– vincent, Commented Oct 24, 2020 at 12:55

Tibos · Accepted Answer · 2013-12-17 14:52:28Z

1

You have iterated one step too far. Simply iterate one step backwards to get a reference to an object and then set the value of the property on that object:

function update(data, fieldName, value) {
    var field = data
    var fieldNameParts = fieldName.split('.');
    while (fieldNameParts.length > 1) // changed number of iterations
        field = field[fieldNameParts.shift()];
    field[fieldNameParts.shift()] = (value === undefined) ? null : value; // set value on property not on variable
}

What you were doing originally was:

var field = data.child.name3;
field = value;

What you want to be doing (and i do in the code above) is:

var field = data.child;
field.name3 = value;

edited Dec 17, 2013 at 14:52

answered Dec 17, 2013 at 14:39

Tibos

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3 Comments

Nathan Rutman Over a year ago

Nice work. I thought I tried that, but I guess I didn't do it correctly. This works, and is better than my solution since it avoids eval(). Thanks!

Nathan Rutman Over a year ago

One small bug: I believe the last line should read field[fieldNameParts.shift()] and not just field[fieldNameParts]...

Tibos Over a year ago

You are technically right. It still works, because the string representation of an array with 1 item (ensured by the while) is usually identical to the string representation of that 1 item. I updated my answer because it was not my intention to use such an obscure feature :), it was just a harmless bug.

Nathan Rutman · Accepted Answer · 2013-12-17 14:45:26Z

0

Ok, I solved this using eval(). While this is a solution, I'm not sure it's the best one. Any additional thoughts?

function update(data, fieldName, value) {
    var evalStr = 'data';
    var fieldNameParts = fieldName.split('.');
    while (fieldNameParts.length)
        evalStr += '[\'' + fieldNameParts.shift() + '\']';
    evalStr += ' = (value === undefined) ? null : value;';
    eval(evalStr);
}

answered Dec 17, 2013 at 14:45

Nathan Rutman

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1 Comment

Nathan Rutman Over a year ago

Interesting module, Robert. If I would have seen that previously, I may have used it instead.

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