Trim JavaScript object to specified properties with matching values

Question

I am trying to verify that an object has a certain set of properties and that their values are of a certain type. I'd like to be able to compare an object to a template like

name: "string",
age: "number",
registered: "boolean"

and return an object with only the fields that match the template.

var object = {
    name: "John McClane",
    age: 45,
    location: "Nakatomi Towers",
    registered: "yes"
}

var document = match(object, template);
console.log(document); 

/* Should return 
{
    name: "John McClane",
    age: 45
}
*/

What are the JavaScript best practices in writing a function like this? I'm not too familiar with the built in methods and iteration so I don't want to go about this the wrong way.

There are no specific 'best practices' for this. If writing this, using in and typeof would probably be helpful starts - ignoring edge cases. There is no built-in feature for such a test. There are probably existing 3rd party libraries (FSVO) under the guise of 'JSON schema validation' or similar. — user2864740
– user2864740, Commented Jan 4, 2016 at 1:24
Are you okay with using a library like Underscore or LoDash? Or do you want to stick to plain JavaScript? — Ray Toal
– Ray Toal, Commented Jan 4, 2016 at 1:27

Phil · Accepted Answer · 2016-01-04 01:29:28Z

1

You can use Object.keys to produce an array of template keys, Array.prototype.reduce to iterate over those keys and create a single result object, Object.prototype.hasOwnProperty to test if object has that key and typeof to test the type of object[key].

function match(obj, tpl) {
    return Object.keys(tpl).reduce(function(collection, key) {
        if (obj.hasOwnProperty(key) && typeof obj[key] === tpl[key]) {
            collection[key] = obj[key];
        }
        return collection;
    }, {});
}

answered Jan 4, 2016 at 1:29

Phil

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2 Comments

nem035 Over a year ago

Suggestion: typeof might not work for all cases, for instance null. Something like this should probably be the type matching function

Phil Over a year ago

@nem true. If OP wants to test for types like Array, typeof isn't going to cut it either but given the sample of "string", "number" and "boolean", it should suffice

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