How to loop through specific keys in nested object?

Question

I want to pull specific parts (definitely not all) from this object:

var metadata = {
    cat: {
        id: 'id',
        name: 'kitty',

    },    
    dog: {
        id: 'id',
        name: 'spot',
        owner: {
            name: 'ralph',
        }
    }    
    //tons of other stuff
};

I would like to do something like this:

var fields = ['cat.id', 'dog.name', 'dog.owner.name'];
fields.forEach( function(key) {
    console.log(metadata[key]); //obv doesn't work
});

This is a simplified scenario where I'm trying to validate specific fields in metadata. Is there a straightforward way to do this?

elclanrs · Accepted Answer · 2014-08-20 22:29:40Z

2

Split the path to extract individual keys, then use a reducer to resolve the value, then map the results:

var path = function(obj, key) {
  return key
    .split('.')
    .reduce(function(acc, k){return acc[k]}, obj)
}

var result = fields.map(path.bind(null, metadata))
//^ ['id', 'spot', 'ralph']

Now you can log them out if you want:

result.forEach(console.log.bind(console))

answered Aug 20, 2014 at 22:29

elclanrs

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4 Comments

WBC Over a year ago

sorry I can't seem to follow what the code is doing, would you mind explaining a bit? I've worked with the individual functions but can't seem to piece them together like you've done.

elclanrs Over a year ago

What exactly don't you understand? What method in particular?

WBC Over a year ago

I don't understand the path.bind part. Is this how the flow goes? In fields.map, a field, say, 'cat.id' gets passed to path, and reduce calls metadata[cat], metadata[cat][id], finally returns that value? Why is path.bind(null) necessary?

elclanrs Over a year ago

map expects a function; bind partially applies a function where this is the first argument which is not needed, thus null. You could write it with an extra anonymous function: fields.map(function(x){return path(metadata, x)}).

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