How do I enumerate the properties of a JavaScript object? [duplicate]

Asked
Active3 hr before
Viewed126 times

7 Answers

duplicateobjectjavascript
90%

How do I enumerate the properties of a JavaScript object?,Here's how to enumerate an object's properties:,In modern browsers (ECMAScript 5) to get all enumerable properties you can do:,I'm still a beginner in JavaScript, but I wrote a small function to recursively print all the properties of an object and its children:

Simple enough:

for (var propertyName in myObject) {
   // propertyName is what you want
   // you can get the value like this: myObject[propertyName]
}
load more v
88%

I actually want to list all the defined variables and their values, but I've learned that defining a variable actually creates a property of the window object.,I found it... for (property in object) { // do stuff } will list all the properties, and therefore all the globally declared variables on the window object..,I'm still a beginner in JavaScript, but I wrote a small function to recursively print all the properties of an object and its children:,Now, that said, hasOwnProperty() is useful for filtering, but we don't need to sound a warning as if there is something dangerous in getting inherited properties.

Simple enough:

for (var propertyName in myObject) {
   // propertyName is what you want
   // you can get the value like this: myObject[propertyName]
}
load more v
72%

For deep cloning, we need to use alternatives, because Object.assign() copies property values. ,If the source value is a reference to an object, it only copies the reference value.,Object.prototype.valueOf(),Both String and Symbol properties are copied.

Object.assign(target, ...sources)
load more v
65%

let person = [{
   name: "john"
}, {
   name: "jane"
}, {
   name: "imelda"
}, {
   name: "john"
}];

function removeDuplicates(data, key) {

   return [
      ...new Map(data.map(item => [key(item), item])).values()
   ]

};

console.log(removeDuplicates(person, item => item.name));
load more v
75%

Objects are the fundamental blocks of JavaScript. An object is a collection of properties, and a property is an association between a key (or name) and a value. Almost all objects in JavaScript are instances of Object which sits on the top of the prototype chain.,Note: Properties on the prototype chain and non-enumerable properties cannot be copied. See here:,property b is a non-enumerable property.,A method is a property of an object that is a function. In the examples so far, we haven’t copied an object with a method. Let’s try that now and use the methods we’ve learnt to make copies.

As you know, the assignment operator doesn’t create a copy of an object, it only assigns a reference to it, let’s look at the following code:

let obj = {
   a: 1,
   b: 2,
};
let copy = obj;

obj.a = 5;
console.log(copy.a);
// Result 
// a = 5;
load more v
40%

Sum all duplicate values in array in JavaScript,How to find duplicate values in a JavaScript array?,Sum all duplicate value in array - JavaScript,Changing value of nested object keys in JavaScript

Suppose, we have a nested object that contains data about some pets like this −

const pets = {
   owner1: 'Frank',
   owner2: 'Curly',
   owner3: 'Maurice',
   dogs: {
      terriers: {
         name1: 'Fido',
         name2: 'Woofy',
         name3: {
            goodDog: 'Frank',
            badDog: 'Judas',
         }
      },
      poodles: {
         name1: 'Curly',
         name2: 'Fido',
      },
   },
};
load more v
22%

Properties of the Object constructor,The code above only copies enumerable properties of mainObj.,Unassigned properties of an object are undefined (and not null).,for...in loops This method traverses all enumerable properties of an object and its prototype chain

var objectName = {} // creating object

objectName.propertyName

var myCar = new Object(); // creating object
myCar.make = 'Ford'; // adding properties to object
myCar.model = 'Mustang';
myCar.year = 1969;
load more v

Other "duplicate-object" queries related to "How do I enumerate the properties of a JavaScript object? [duplicate]"