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.

Answer 1

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.

Answer 2

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.