How to Loop Through or Enumerate a JavaScript Object

How do I loop through or enumerate a JavaScript object?

You can use the for-in loop as shown by others. However, you also have to make sure that the key you get is an actual property of an object, and doesn't come from the prototype.

Here is the snippet:

var p = {    "p1": "value1",    "p2": "value2",    "p3": "value3"};
for (var key in p) {    if (p.hasOwnProperty(key)) {        console.log(key + " -> " + p[key]);    }}

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]]);
}

How do I loop through Javascript object checking key and values?

Good answer from @doctorgu, you could also you some.

const string = 'Simplexity'

const mapping = {
  'Mind Management': {
    type: 'average',
    linked_topics: ['Digital Detox', 'Small Scaling', 'Simplexity'],
    edge: 'Zeroed Out'
  },
  'Ancient Wisdom': {
    type: 'direct',
    edge: 'Roots Revival'
  }
}

const isStringInMapping = Object.entries(mapping).some(([key, value]) => (
    key == string || value.linked_topics?.includes(string)
))

console.log(isStringInMapping)

How do I loop through or enumerate a JavaScript object?

You can use the for-in loop as shown by others. However, you also have to make sure that the key you get is an actual property of an object, and doesn't come from the prototype.

Here is the snippet:

var p = {    "p1": "value1",    "p2": "value2",    "p3": "value3"};
for (var key in p) {    if (p.hasOwnProperty(key)) {        console.log(key + " -> " + p[key]);    }}

Looping through object properties, one of which is an array (JS)

This will loop through each key (e.g. color, make, etc.) of your car object, and print the key and the value.

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

Will output the following:

color red
make Chevrolet
model Camaro
year 1967
options [ 'hard top', 'power windows', 'racing stripe', 'fog lights' ]

How to loop through a plain JavaScript object with the objects as members

for (var key in validation_messages) {
    // skip loop if the property is from prototype
    if (!validation_messages.hasOwnProperty(key)) continue;

    var obj = validation_messages[key];
    for (var prop in obj) {
        // skip loop if the property is from prototype
        if (!obj.hasOwnProperty(prop)) continue;

        // your code
        alert(prop + " = " + obj[prop]);
    }
}

Looping through an object and changing all values

try

var superSecret = function(spy){
  Object.keys(spy).forEach(function(key){ spy[key] = "redacted" });
  return spy;
}

How can I loop through a JavaScript object array?

It appears you may just have missed the "messages" property in the data, so the loop is likely iterating the root Object rather than the Array:

for (var key in data.messages) {
    var obj = data.messages[key];
    // ...
}

Unless data was set to messages before the given snippet.

Though, you should consider changing that to a normal for loop for the Array:

for (var i = 0, l = data.messages.length; i < l; i++) {
    var obj = data.messages[i];
    // ...
}

How to Loop Through or Enumerate a JavaScript Object

How do I loop through or enumerate a JavaScript object?

How to iterate over a JavaScript object?

How do I loop through Javascript object checking key and values?

How do I loop through or enumerate a JavaScript object?

Looping through object properties, one of which is an array (JS)

How to loop through a plain JavaScript object with the objects as members

Looping through an object and changing all values

How can I loop through a JavaScript object array?

Related Topics

Leave a reply