How to iterate over a JavaScript object in parts?

General Discussions
#1

How can I iterate over a JavaScript object? I have an object in JavaScript that looks like this:

{
    abc: '...',
    bca: '...',
    zzz: '...',
    xxx: '...',
    ccc: '...',
    // ...
}

I want to use a for loop to access its properties, but I would like to iterate in parts instead of processing all the object properties at once. For example, with a simple array, I can do it with a standard for loop like this:

for (i = 0; i < 100; i++) { ... } // first part
for (i = 100; i < 300; i++) { ... } // second part
for (i = 300; i < arr.length; i++) { ... } // last

How can I achieve this with a JavaScript iterate object?

#2

Hello! Smrity

When it comes to iterating over the keys of arrays, strings, or objects in JavaScript, there are several ways to approach it. One common method is using the for...in loop:

javascript

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

If you’re working with ES6 and need both keys and values simultaneously, you can use Object.entries():

javascript

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

To ensure that only the object’s own properties are logged (and not inherited ones), it’s a good practice to include a check with hasOwnProperty:

javascript

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

However, if you’re working with a simple object that you’ve created, this extra check might not be necessary.

For more information on managing objects and their properties, you can always refer to the MDN documentation.

In cases where you want to iterate “in chunks” over the keys, you can first extract the keys into an array using:

javascript

let keys = Object.keys(yourObject);

For broader compatibility across different environments, you might prefer a method like this:

javascript

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

Finally, if you need to iterate over specific chunks of the properties, you can use the indices:

javascript

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

This method is especially useful when working with large objects or when you want more control over the iteration.

Best regards,

#3

Dear Smrity,

Using Object.keys() with forEach: You can retrieve the keys of the object and use the forEach method to iterate through them:

Object.keys(yourObject).forEach(key => { console.log(key, yourObject[key]); });

This approach simplifies the code and is quite readable.