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.

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.

• javascript
• json
• regex

• 2 The simpler/efficient way is to iterate the keys. – user4227915 Commented Oct 19, 2015 at 15:32
• surely you just do for (... in ..) and then test against regex each time... – Callum Linington Commented Oct 19, 2015 at 15:32
• 1 That looks like a JavaScript object, but not JSON. – Biffen Commented Oct 19, 2015 at 15:32
• 1 @WashingtonGuedes Yes, that's its name. But JSON has a different syntax, patible with, but not the same as, JavaScript. In this case the names are missing quotes. – Biffen Commented Oct 19, 2015 at 15:34
• 1 @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 Commented Oct 19, 2015 at 15:34

2 Answers 2

As mentioned in the ments, 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)

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);