How to check if a JavaScript Object has a property name that starts with a specific string?

Question

Lets say I have javascript objects like this one:

var obj = {
    'addr:housenumber': '7',
    'addr:street': 'Frauenplan',
    'owner': 'Knaut, Kaufmann'
}

How can I check if the object has a property name that starts with addr? I’d imagine something along the lines of the following should be possible:

if (e.data[addr*].length) {

I tried RegExp and .match() to no avail.

Amit Joki · Accepted Answer · 2014-12-16T15:13:29.413

48

You can check it against the Object's keys using Array.some which returns a bool.

if(Object.keys(obj).some(function(k){ return ~k.indexOf("addr") })){
   // it has addr property
}

You could also use Array.filter and check it's length. But Array.some is more apt here.

edited Dec 16 '14 at 15:13

answered Dec 16 '14 at 14:45

Amit Joki

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Cheers to all! This one seems to be the shortest and most elegant way to do it. – Alexander Rutz Dec 16 '14 at 14:56
@Edwin brilliant, even more elegant! – Alexander Rutz Dec 16 '14 at 15:19
lol alright soon it'll be easier with fat arrow functions in ES6 – Edwin Reynoso Dec 16 '14 at 15:20
4

@Edwin yeah.. `Object.keys(obj.some((k) => ~k.indexOf("addr"));`. Waiting for it to come :) – Amit Joki Dec 16 '14 at 15:21
Me too Me too can't wait – Edwin Reynoso Dec 16 '14 at 15:25
What is the role of ~ here? – zookastos Jan 30 '17 at 04:30
3

Note that with a very large object, it's not very efficient because `Object.keys()` is generated before the call with `some()`; it's more efficient to check property by property with a `for in`. – Skywalker13 Mar 20 '18 at 11:23

score 12 · Answer 2 · answered Dec 16 '14 at 14:45

You can use the Object.keys function to get an array of keys and then use the filter method to select only keys beginning with "addr".

var propertyNames = Object.keys({
    "addr:housenumber": "7",
    "addr:street": "Frauenplan",
    "owner": "Knaut, Kaufmann"
}).filter(function (propertyName) {
    return propertyName.indexOf("addr") === 0;
});
// ==> ["addr:housenumber", "addr:street"];

This gives you existence (propertyNames.length > 0) and the specific names of the keys, but if you just need to test for existence you can just replace filter with some.

score 6 · Answer 3 · answered Dec 16 '14 at 14:47

6

Obj = {address: 'ok', x:5}

Object.keys(obj).some(function(prop){
  return ~prop.indexOf('add')
}) //true

answered Dec 16 '14 at 14:47

Edwin Reynoso

1,511
9
18

2

What is the Tilders functionality here? – Sweet Chilly Philly Jun 28 '20 at 22:43

Termininja · Answer 4 · 2021-04-16T10:12:57.477

1

You can check this also with startsWith():

Object.keys(obj).some(i => { return i.startsWith('addr') })

edited Apr 16 '21 at 10:12

answered Apr 16 '21 at 08:39

Termininja

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score 0 · Answer 5 · answered Dec 16 '14 at 14:44

Try this:

var myObject = {
    'prop1': 'value1',
    'xxxxx': 'value2'
};

var stringToCheck = 'addr';

for(var propertyName in myObject) {
    var x = propertyName.substr(0, stringToCheck.length - 1);

    if(x == stringToCheck) {
        return true;
    }
}

score 0 · Answer 6 · answered Dec 16 '14 at 14:52

I don't think "Querying" a object properties is possible. You would have to loop through the properties individually and determine if they match. something like this...

function findProp(e, prop)
{
    for(var o in e.data){
        if(o.substr(0, prop.length)==prop) //<- you could try the regex or match operation here
            return true;
    }
    return false;
}

alert(findProp({data:{addr:{street:"a", sub:"b"}}}, 'addr'));

You can then process the property if it findProp returns true...

score 0 · Answer 7 · answered Apr 13 '17 at 00:47

0

You can write a function

function check(model) {
   var keys = [];
   for (key in model) { 
       if(key.indexOf("addr") > -1) 
           keys.push(key); 
   }
   return keys;
}

answered Apr 13 '17 at 00:47

Mahib

3,977
5
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Bwyss · Answer 8 · 2018-11-07T22:51:18.770

-1

Why not just

var foo = {'bar':'funtimes'};
if (foo.bar.includes('fun')) {
  console.log('match');
}

edited Nov 07 '18 at 22:51

answered Nov 07 '18 at 22:39

Bwyss

1,736
3
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1

Because it is regarding the key, not the value. – Erwin Lengkeek Jan 29 '19 at 08:27

How to check if a JavaScript Object has a property name that starts with a specific string?

8 Answers8