How to Iterate Through JavaScript Objects

javascriptobject

I'm having a really hard time trying to find a way to iterate through this object in the way that I'd like. I'm using only Javascript here.

First, here's the object

{
"dialog":
{
    "dialog_trunk_1":{
        "message": "This is just a JSON Test"
    },
    
    "dialog_trunk_2":{
        "message": "and a test of the second message"
    },

    "dialog_trunk_3":
    {
        "message": "This is a test of a bit longer text. Hopefully this will at the very least create 3 lines and trigger us to go on to another box. So we can test multi-box functionality, too."
    }
}
}

Right now, I'm just trying basic ways to get through to each dialog_trunk on this object. I ideally want to loop through the object and for each trunk, display it's message value.

I've tried using a for loop to generate the name/number of the dialog_trunk on the fly, but I can't access the object using a string for the object name so I'm not sure where to go from here.

Best Answer

You use a for..in loop for this. Be sure to check if the object owns the properties or all inherited properties are shown as well. An example is like this:

var obj = {a: 1, b: 2};
for (var key in obj) {
  if (obj.hasOwnProperty(key)) {
    var val = obj[key];
    console.log(val);
  }
}

Or if you need recursion to walk through all the properties:

var obj = {a: 1, b: 2, c: {a: 1, b: 2}};
function walk(obj) {
  for (var key in obj) {
    if (obj.hasOwnProperty(key)) {
      var val = obj[key];
      console.log(val);
      walk(val);
    }
  }
}
walk(obj);

Related Solutions

JavaScript – How to Iterate Over a JavaScript Object

For iterating on keys of Arrays, Strings, or Objects, use for .. in :

for (let key in yourobject) {
  console.log(key, yourobject[key]);
}

With ES6, if you need both keys and values simultaneously, do

for (let [key, value] of Object.entries(yourobject)) {
    console.log(key, value);
}

To avoid logging inherited properties, check with hasOwnProperty :

for (let key in yourobject) {
   if (yourobject.hasOwnProperty(key)) {
      console.log(key, yourobject[key]);
   }
}

You don't need to check hasOwnProperty when iterating on keys if you're using a simple object (for example one you made yourself with {}).

This MDN documentation explains more generally how to deal with objects and their properties.

If you want to do it "in chunks", the best is to extract the keys in an array. As the order isn't guaranteed, this is the proper way. In modern browsers, you can use

let keys = Object.keys(yourobject);

To be more compatible, you'd better do this :

 let keys = [];
 for (let key in yourobject) {      
     if (yourobject.hasOwnProperty(key)) keys.push(key);
 }

Then you can iterate on your properties by index: yourobject[keys[i]] :

for (let i=300; i < keys.length && i < 600; i++) { 
   console.log(keys[i], yourobject[keys[i]]);
}

Best Answer

Related Solutions

JavaScript – How to Iterate Over a JavaScript Object

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