JavaScript: How can I get all the keys and values of an object that begin with a specific string?

Question

I am trying to get all the keys and values of an object that begin with imageIds.

My object appears as the following:

{
    title: 'fsdfsd',
    titleZh: 'fsdfsd',
    body: 'fsdf',
    bodyZh: 'sdfsdf',
    imageIds: '/uploads/tmp/image-3.png',
    imageIdsZh: '' 
}

but I only need the properties imageIds, and imageIdsZh. However tomorrow, a object might contain imageIdsBlah and I would need to pick it up as well. I could remove the first few properties from the object, but then the next object might contain additional properties such as foo: 'bar'

Answer 1

Some functional style awesomeness:

var data = {
    title: 'fsdfsd',
    titleZh: 'fsdfsd',
    body: 'fsdf',
    bodyZh: 'sdfsdf',
    imageIds: '/uploads/tmp/image-3.png',
    imageIdsZh: '' 
};

var z = Object.keys(data).filter(function(k) {
    return k.indexOf('imageIds') == 0;
}).reduce(function(newData, k) {
    newData[k] = data[k];
    return newData;
}, {});

console.log(z);

Demo: http://jsfiddle.net/ngX4m/

Some minor explanation:

1. We use Array.prototype.filter() function to filter out the keys that start with `imageIds2
2. We use Array.prototype.reduce() to convert an array of filtered keys into an object of key-value pairs. For that we use the initial value of {} (an empty object), fill it and return from every execution step.

UPD:

A fair update from @GitaarLAB:

Object.keys is ES5, but returns an objects own properties (so no need for obj.hasOwnProperty(key))

Answer 2

Depending on how large the object is, this may not scale well, but it will work

for(key in obj){
   if(obj.hasOwnProperty(key)){
      if(key.indexOf("imageIds")===0){
        //do something
      }
   }
}

Answer 3

Along the lines of the answer from @zerkms, I've been working on a functional programming library for Javascript. With the tools from that library, this turns into a (somewhat dense) one-liner:

var data = {
    title: 'fsdfsd',
    titleZh: 'fsdfsd',
    body: 'fsdf',
    bodyZh: 'sdfsdf',
    imageIds: '/uploads/tmp/image-3.png',
    imageIdsZh: '' 
};

var x = pick(filter(compose(eq("imageIds"), substring(0,8)), keys(data)), data);
console.log(x);

This code is not necessarily any better than what @zerkms posted, but it does show off some more of the power of functional abstractions beyond the few that are built into Array.prototype.

You can see it in action on JSFiddle.