Get all JSON keys that match a pattern

Question

Javascript in a browser environment. I wish to get all keys in a JSON object that match a specific pattern. Say, all of them that begin with mystring. Is there a simpler/efficient way of doing that without having to iterate through all the keys ?

{
   somekey1: "someval1",
   somekey2: "someval2",
   mystringkey1: "someval",
   mystringkey2: "someval"

}

There had been similar questions, but a) doesn't fully answer this question and b) JQuery is not an option at the moment.

surely you just do `for (... in ..)` and then test against regex each time... — Callum Linington, Oct 19 '15 at 15:32
@WashingtonGuedes Yes, that's its name. But JSON has a different syntax, compatible with, but not the same as, JavaScript. In this case the names are missing quotes. — Biffen, Oct 19 '15 at 15:34
@WashingtonGuedes The OP's code does not conform to the JSON grammar; it is not JSON. It *does* conform the JavaScript grammar for objects, however. — apsillers, Oct 19 '15 at 15:34
The ES5 way would be something like `Object.keys(yourObjectHere).filter(function(key){return (/^mystring/i).test(key);})`. — Sebastian Simon, Oct 19 '15 at 15:35

Kristján · Accepted Answer · 2015-10-19T15:54:35.447

5

As mentioned in the comments, iterate through your object and add to a result when you find a matching key.

var data = {
   somekey1: "someval1",
   somekey2: "someval2",
   mystringkey1: "someval",
   mystringkey2: "someval"
}

var filtered = {}

for (key in data) {
    if (key.match(/^mystring/)) filtered[key] = data[key];
}

console.log(filtered)

edited Oct 19 '15 at 15:54

answered Oct 19 '15 at 15:35

Kristján

18,165
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AmmarCSE · Answer 2 · 2015-10-19T15:43:13.270

3

Use Object.keys and filter

var myObj = {
  somekey1: "someval1",
  somekey2: "someval2",
  mystringkey1: "someval",
  mystringkey2: "someval"

};

var pattern = /^mystring/;
var matchingKeys = Object.keys(myObj).filter(function(key) {
  return pattern.test(key);
});

console.log(matchingKeys);

edited Oct 19 '15 at 15:43

answered Oct 19 '15 at 15:35

AmmarCSE

30,079
5
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Get all JSON keys that match a pattern

2 Answers2