Loop through JSON objects that only start with a certain pattern

Question

What is the correct/idiomatic way to loop through JSON objects that only start with a certain pattern?

Example: say I have a JSON like

{
  "END": true, 
  "Lines": "End Reached", 
  "term0": {
    "PrincipalTranslations": {
      // nested data here
    }
  },
  "term1": {
    "PrincipalTranslations": {
      // more nested data here
    }
  }
}

I only want to access the PrincipalTranslations object and I tried with:

$.each(translations, function(term, value) {
    $.each(term, function(pos, value) {
        console.log(pos);
    });
});

Which doesn't work, possibly because I can't loop through the END and Lines objects.

I tried to go with something like

$.each(translations, function(term, value) {
    $.each(TERM-THAT-STARTS-WITH-PATTERN, function(pos, value) {
        console.log(pos);
    });
});

using wildcards, but without success. I could try to mess up with if statements but I suspect there is a nicer solution I'm missing out on. Thanks.

you can't use wildcards there, $.each simply loops over an array or an object's keys. You'll have to do the filtering using something else, such as an if statement. — Kevin B, Jun 02 '14 at 15:39
If possible, it would be much easier to change your JSON structure. Can you change the format to contain an array of `terms` instead of each having it's own property? — Rory McCrossan, Jun 02 '14 at 15:40
FYI, `value` will be the object to iterate over, `term` is the property name. Check the documentation: http://api.jquery.com/jquery.each/ — Felix Kling, Jun 02 '14 at 15:43
I get that JSON as a result of an API request so yep, I could re-arrange the whole thing backend-side. Since I'm new to web dev I just assumed the API was right and the problem was me though :] — laurids, Jun 02 '14 at 15:51

score 3 · Accepted Answer · answered Jun 02 '14 at 15:46

If you're only interested in the PrincipalTranslations-objects, following would do the trick:

$.each(translations, function(term, value) {
    if (value.PrincipalTranslations !== undefined) {
        console.log(value.PrincipalTranslations);
    }
});

JSFiddle

Dalorzo · Answer 2 · 2014-06-02T15:56:32.837

1

How I would search for a property in an object it is like this:

var obj1 ={ /* your posted object*/};


// navigates through all properties
var x = Object.keys(obj1).reduce(function(arr,prop){
// filter only those that are objects and has a property named "PrincipalTranslations"
    if(typeof obj1[prop]==="object" &&  Object.keys(obj1[prop])
        .filter(
            function (p) {
                return p === "PrincipalTranslations";})) {
                     arr.push(obj1[prop]);
                }
    return arr;
},[]);

console.log(x);

edited Jun 02 '14 at 15:56

answered Jun 02 '14 at 15:51

Dalorzo

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That's interesting, thanks. If I decide to rearrange the API response, would you say is better to do it client-side as in your example or server-side? – laurids Jun 02 '14 at 15:54
@laurids this works on any browser older than IE9 and if you polyfill on any browser – Dalorzo Jun 02 '14 at 15:55
actually I was more concerned about which one is the "good practice" rather than portability ;) – laurids Jun 02 '14 at 15:59
This approach uses ES5 standards. If you want to use jQuery, Underscore or lodash it will depend on the library to provide "portability" probably about the same coverage these days. – Dalorzo Jun 02 '14 at 16:02

Loop through JSON objects that only start with a certain pattern

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