javascript use variable as object key

In JavaScript, objects can play two roles (always at least one of them, sometimes mixtures): Records: A fixed amount of properties that are known at development time. var y = new Number (); // Declares y as a Number object. Let’s use Object.keys () to get the keys of hero object: const hero = { name: 'Batman', city: 'Gotham' }; Object.keys(hero); Object.keys (hero) returns the list ['name', 'city'], which, as expected, are the keys of … Object.keys () method is used to return an array whose elements are strings corresponding to the enumerable properties found directly upon an object. ; Use array methods on that array, e.g. map, filter and others. But we can also access the value using a variable key. To create a JavaScript alert that shows us the value associated with the key first_name in a pop-up, we can do so by calling the JavaScript alert () function: alert(sammy.first_name); Output. A variable that refers to an object must be a Variant, an Object, or a specific type of object. The JavaScript typeof Operator. In order to set an object’s key by variable, here are few steps to follow. Avoid String, Number, and Boolean objects. This makes code more readable. Use the typeof operator to get the type of an object or variable in JavaScript. An object is a collection of key-value pairs. To simplify I've removed . map. A property is a “key: value” pair, where key is a string (also called a “property name”), and value can be anything. Written politely 2018-06-22.Problem: So, you want to use a variable to dynamically generate a key in a javascript object? a variable) returning a value.. As objects are variables, you can instantiate them the same way as a variable. There are better ways to actually generate this JSON data consists of key/value pairs similar to JavaScript object properties. Javascript Object Oriented Programming Front End Technology. Declare an object variable. ES2015 introduced two important new JavaScript keywords: let and const. Compare it with a cup, for example. How to run shell script file or command using Nodejs? The order of the keys in the final list is the order they appear in the original Object. Let’s use Object.keys() to get the keys of hero object: const hero = { name : 'Batman' , city : 'Gotham' } ; Object . var z = new Boolean (); // Declares z as a Boolean object. How to use a variable for a key in a JavaScript object literal? Here’s how you can declare an object with the new ES6 / ES2015 syntax: Method 2 should be used in most cases as it gives clean syntax and method 1 should only be used in case of no es6 support. When interacting with a database, especially document based databases, we can often find ourselves in situations where the keys in the database may change, depending on client side conditions. for in loop helps us to get the object key on each iteration by using that we can access … Now you know how to set an object key using a variable in javascript. Solution: It is actually pretty simple. A key of an object must be a string or a symbol, you cannot use an object as a key. All operations via copied references (like adding/removing properties) are performed on the same single object. Your email address will not be published. These two keywords provide Block Scope variables (and constants) in JavaScript. However, using an object as a map has some side effects: An object always has a default key like the prototype. If we’d like to apply them, then we can use Object.entries followed by Object.fromEntries:. Dot notation is used most frequently. Javascript Object Oriented Programming Front End Technology. Use Object.entries(obj) to get an array of key/value pairs from obj. Instead, JavaScript treats $ and _ as if they were letters of the alphabet. Syntax: var key="your_choice"; var object = {}; object[key] = "your_choice"; console.log(object); With ECMAScript 2015 you are now able to do it directly in object declaration with the brackets notation: . So, If the property name is not a valid… The key and values are written in double quotes separated by a colon : . a variable) returning a value.. If Try to install Nix package Manager on Window Subsystem for Linux or WSL, it throws some cryptic error messages, But There is work around for installing Nix On WSL Ubuntu or any…, If you ever wanted to run some automation script or file in your Unix/Linux machine using nodejs? Transforming objects. The object values can be retrieved using object.values() method.The return keys/values ordering is same as provided object. Use Object.fromEntries(array) on the resulting array to turn it back into an object. This is the most popular and most used way of accessing the property of an object. Die Reihenfolge der Eigenschaften ist die … It is similar to array destructuring except that instead of values being pulled out of an array, the properties (or keys) and their corresponding values can be pulled out from an object. var key = 'top'; $('#myElement').animate( (function(o) { o[key]=10; return o;})({left: 20, width: 100}), 10 ); key is the name of the new property. Assign the object variable to an object. With ES6, you can now directly use a variable as your property key in your object literal. JavaScript set object key using variable (es6 & es5) Sometimes you want assign key to your js object, that key is dynamic, coming from database or user input etc, you can’t define it as normal object key, for doing this we will see multiple methods including new es6 method on how to use a variable as an object property or key in javascript. Before ES2015, JavaScript had only two types of scope: Global Scope and Function Scope. #How to Set Dynamic Property Keys with ES6 Previously, we had to do 2 steps - create the object literal and then use the bracket notation. Use the Object.keys() method to retrieve all of the key names from an object. name ) ; //output-> king123 Using Javascript Maps. ; The second one has the name "age" and the value 30.; The resulting user object can be imagined as a cabinet with two signed files labeled “name” and “age”. Using Dot and Bracket Notations Example. However, this is a naive approach where we check for every key through the object to match its value. A cup has a color, a design, weight, a material it is made of, etc. Then in the JavaScript, we could say: let newObjectKey = document.getElementById ("fm").getAttribute ('value'); Then, after the userA updates their favorite food, we could recreate the object, and update the object on the server, using the above variable as the object key. Example-1: This example sets the object key by variable key and then inserts {“GFG_key”:”GFG_Val”} object to a array. 3. Object.keys(object) is a utility function that returns the list of keys of object. Husband, father, teacher, musician, avid gamer, nature enthusiast, and passionate about the human condition. This is very popular JavaScript method for object.You can get any object keys using object.keys() method. JavaScript objects are collections of key-value pairs, where each object key (also called object property) has a specific value. A Map object iterates its elements in insertion order — a for...of loop returns an array of [key, value]for each iteration. The variable sammy is first, followed by a dot, followed by the key to be accessed. This will not delete the item it will just update. The variable name must match the property (or keys) name of the object. Using a variables as an object key is a common requirement. javascript node.js. Defining an object literal is the simplest way to create a JavaScript object. Global Scope. In the user object, there are two properties:. 3 min read. In this tutorial, we are going to learn about using the variable as a key in a JavaScript object literal with the help of examples. Using a variable as a key in an object literal in Javascript ES6. As you know, we can create an object of any function using the new keyword. A property has a key (also known as “name” or “identifier”) before the colon ":" and a value to the right of it.. keys ( hero ) ; // => ['name', 'city'] var obj = { [key]: value } Where key can be any sort of expression (e.g. Introduction to JavaScript Map object. The objects they identify include things such as variables, functions, properties, events, and objects. However, using an object as a map has some side effects: An object always has a default key like the prototype. Using JavaScript Variables as Object Keys. New in JavaScript with ES6/ES2015, if you want to define an object who's keys have the same name as the variables passed-in as properties, you can use the shorthand and simply pass the key name. In the above object, if you want to add another country code that coming from another variable instead of a direct key, then you can’t directly give a variable name in key, instead, you have to use one of the following methods. For example, If you want to use a default string append or prepend, that is simple, too using ES6. How to access an object value using variable key in JavaScript? JavaScript Let Previous Next ECMAScript 2015. First way const username = "name" ; const obj = { [ username ] : "king123" } console . Dictionaries: An arbitrary amount of properties whose names are not known at development time. Sometimes you want to know the type of an object to perform some action on it. Let's look over them in a nutshell. A cup is an object, with properties. variable to get the elements of an array. If you want to use a default string append or prepend, that is simple, too using ES6. Here is how you use it when you're evaluating the type of … const courses = { java: 10, javascript: 55, nodejs: 5, php: 15 }; // convert object to key's array const keys = Object.keys(courses); // print all keys console.log(keys); // [ 'java', 'javascript', 'nodejs', 'php' ] // iterate over object keys.forEach((key, index) => { console.log(`${key}: ${courses[key]}`); }); // java: 10 // javascript: 55 // nodejs: 5 // php: 15 Last Updated : 31 Oct, 2019 In ES5 and earlier, you could not use a variable as a property name inside an object literal. Object keys can be dynamically assigned in ES6 by placing an expression in square brackets. An object can be created with figure brackets {…} with an optional list of properties. We know that an object value can be accessed by using a Dot notation or Bracket notation. Here are few of the examples. In this following example, we will change the Name key value to Elif and 10 key value to ten. It evaluates the type of the operand and returns the result as a string. For this reason, these characters are not treated the same way as other special symbols. So here your code would look like: .stop().animate({ [thetop]: 10 }, 10) Where thetop will be evaluated before being used as key. This quick JavaScript tutorials help to understand usage of Object.keys() method with example. We know that an object value can be accessed by using a Dot notation or Bracket notation. ES6 provides a new collection type called Map that addresses these deficiencies. How to access an object value using variable key in JavaScript? Assign that variable a value. Vithal Reddy is a seasoned technology professional with expertise in Full Stack Web development, Micro services and Scaling infrastructure on Cloud. Objects are variables too. I have the following code that is supposed to call an api using the object key value and then open a text file and replace the text that matches the key with the API data. You could use any value as the variableKeyArray, but this example show how to use a Numbers, and Booleans as Objects! If it does not match, then it receives an undefinedvalue. So here your code would look like: .stop().animate({ [thetop]: 10 }, 10) Where thetop will be replaced by the variable value. This is how JavaScript knows which property of the object we want to assign. Use the Dim statement or one of the other declaration statements (Public, Private, or Static) to declare an object variable. function _defineProperty(obj, key, value) { if (key in obj) { Object.defineProperty(obj, key, { value: value, enumerable: true, configurable: true, writable: true }); } else { obj[key] = value; } return obj; } var bar = "b"; var foo = _defineProperty({}, bar, "Orson oson a borsos borsós fosos koros boros korsón"); Object.keys(runner); If you print the result, you’ll get an array of the object’s keys. The following screen shot illustrates assigning values to objects using the node command line. Required fields are marked *. Steps: First make a variable. Wrap your key name in [] and you should be good to go. code, but this implementation is just to illustrate the use of a variable as a key in an Objects in JavaScript, just as in many other programming languages, can be compared to objects in real life. An object does not have a property that represents the size of the map. we will create an object first and then we will use to add a dynamic key or property to javascript object, In es6 we can direct use inside an object. Object.keys () liefert ein Array, dessen Elemente Strings sind, welche die aufzählbaren Eigenschaften des Objekts respräsentieren. The JavaScript Object.keys () method retrieves the keys in an Object and returns a list that contains those keys. The object of properties passed to animate will be {left: 20, width: 100, top: 10} This is just using the required [] notation as recommended by the other answers, but with fewer lines of code! JavaScript MCQ (Multi Choice Questions) with javascript tutorial, introduction, javascript oops, application of javascript, loop, variable, objects, map, typedarray etc. var obj = { [key]: value } Where key can be any sort of expression (e.g. To access the data we encounter the same problems without quotes. The only option you had was to create the object literal, assign the variable property name with value and pass the resulting object to the animate method. It can hold both the object or primitive type of key-values. Wrap your key name in [] and you should be good to go. Variables declared Globally (outside any function) … So copying such a variable or passing it as a function argument copies that reference, not the object itself. When destructuring the objects, we use keys as the name of the variable. console.log(Object.keys(runner)); //Result: [ 'name', 'age', 'milesPerWeek', 'race' ] In other words, a variable stores not the “object value”, but a “reference” (address in memory) for the value. We'll call this on an array of keys that we can get using the Object.keys() method that returns us all the keys of an object. We can use the find() method to compare keys to have a certain value that we want to find. Using Variables as Keys. The Object.keys () method returns an array of a given object's own enumerable property names, iterated in the same order that a normal loop would. JavaScript Objects HTML DOM Objects. With ECMAScript 2015 you are now able to do it directly in object declaration with the brackets notation: . log ( obj . For in loop. It returns the key, value pair in the same order as inserted. So, you want to use a variable to dynamically generate a key in a javascript object? Object.keys (object) is a utility function that returns the list of keys of object. Your email address will not be published. Then make a object. The typeof operator takes only one operand (a unary operator). But objects can contain many values. But we can also access the value using a variable key. Let's try to do it this way, The concept of objects in JavaScript can be understood with real life, tangible objects.In JavaScript, an object is a standalone entity, with properties and type. object literal in JavaScript. We can also change an existing item value by using its key. The ordering of the properties is the same as that given by the object manually in a loop is applied to the properties. S key by variable, here are few steps to follow accessed by using a variables as object! ) in JavaScript, objects penetrate almost every aspect of the variable sammy is first, followed the! Too using ES6 der Eigenschaften ist die … using JavaScript variables as an object variable husband, father,,. We use keys as the name key value to ten the same without. Or passing it as a string or a specific value for a key in a JavaScript object.. } console a javascript use variable as object key as object keys reference, not the object manually in a loop is applied the... Understand usage of object.keys ( ) method retrieves the keys in the original object die. Scope variables ( and constants ) in JavaScript is a utility function that the... ( array ) on the same single object in a loop is applied to the enumerable found... One operand ( a unary operator ) way to create a JavaScript object the grammar object. From obj it receives an undefinedvalue use array methods on that array, e.g the popular... Easily conquer JavaScript it as a map has some side effects: an object value can any. ’ s keys will not delete the item it will just update followed by the key value! Computedpropertyname ’ as part of the keys in the same problems without quotes the language next... Manually in a loop is applied to the properties the other declaration (...: object.keys ( object ) is a utility function that returns the list of properties whose names are not at. A JavaScript object will just update illustrates assigning values to objects using the Node command.. Private, or Static ) to declare an object value using variable key objects, will... _ as if they were letters of the key and values are written in quotes... The objects, we use keys as the name of the grammar for object literals, which helps a. Action on it Variant data type, there are two properties: value using a variable key JavaScript... Directly upon an object value using variable key in a JavaScript object or Bracket.. Key value to ten two important new JavaScript keywords: let and const value be. And _ as if they were letters of the object values can be any sort of expression ( e.g name! First way const username = `` name '' ; const obj = [! Returns the result as a map has some side effects: an object value a. Json data consists of key/value pairs from obj treats $ and _ if. Two main parts: keys and values are written in double quotes separated by a colon.... Value pair in the original object that array, e.g key value to.., Private, or Static ) to get the type of an object must be a.! Arrays, e.g enthusiast, and passionate about the human condition the type of key-values I comment back! Steps to follow sort of expression ( e.g 2015 you are required to use the typeof to! A utility function that returns the key to be accessed Object.entries ( obj to. Declarations are valid: ' declare MyObject as Variant data type // Declares y as a function argument that. Development time here are few steps to follow development [ for Developers & ]... Is how JavaScript knows which property of the map key by variable, here are few to... Simplest way to create a JavaScript object Declares y as a Boolean object destructuring the,. Before es2015, JavaScript, Medium, Programación can now directly use variable! Public, Private, or Static ) to get the type of an key... Created with figure brackets { … } with an optional list of keys of object simplest... Function argument copies that reference, not the Dot notation before es2015,,. The typeof operator to get an array of key/value pairs from obj the find ( ) ; // = [... } with an optional list of keys of object this quick JavaScript tutorials help to understand usage of object.keys )! As Variant data type welche die aufzählbaren Eigenschaften des Objekts respräsentieren of expression ( e.g any. Key and values z as a map has some side effects: an arbitrary of! It returns the key to be accessed by using its key simple, too ES6. Or one of the alphabet are collections of key-value pairs, Where each object key a! Javascript method for object.You can get any object keys can be dynamically in. Using the Node command line ( like adding/removing javascript use variable as object key ) are performed on the same way a. As a Boolean object refers to an object always has a color a... Variant, an object as a map has some side effects: an key... Match its value these deficiencies returns a list that contains those keys not match, then can! Simplest way to create a JavaScript object now able to do it directly in object declaration the..., Where each object key is a collection of key-value pairs we will change the key. Accessed by using a variable as your property key in a loop is applied the. There are two properties: in your object literal // = > [ 'name ' 'city. Way const username = `` name '' ; const obj = { [ key ]: value Where. The bracketed option and not the object values can be any sort of (... Keys can be accessed by javascript use variable as object key its key item it will just.... Ordering is same as that given by the key, value pair in same! Using Nodejs of object the syntax: object.keys ( runner ) ; // Declares z as Boolean... Ein array, e.g are variables, you want to assign are now able to do it directly in declaration... Use a variable in JavaScript wrap your key name in [ ] and you should be good to.. A new collection type called map that addresses these deficiencies operator ) an array whose elements Strings. Specific type of key-values Web development, Micro services and Scaling infrastructure on Cloud object. Let and const husband, father, teacher, musician, avid gamer nature... The value using variable key in JavaScript, this is very popular JavaScript method for object.You can any. Object can be accessed by using a variable and website in this browser for the next time I comment Stack! Operator to get the type of object result as a key in a JavaScript object )... Object.Values ( ) ; // = > [ 'name ', 'city ' 3. Unary operator ) directly use a variable for a key in a JavaScript object properties know... A naive approach Where we check for every key through the object s. Way to create a JavaScript object properties with an optional list of keys of...., teacher, musician, avid gamer, nature enthusiast, and passionate about the human.. As part of the other declaration statements ( Public, Private, or Static ) to declare an object not... Square brackets a default string append or prepend, that is simple, too using ES6 default string or. Full Stack Web development, Micro services and Scaling infrastructure on Cloud ES6 by placing an expression in square.! Of key/value pairs from obj of keys of object the list of of. Now able to do it directly in object declaration with the brackets notation: hold both object! Not use an object must be a Variant, an object as a argument... We can also change an existing item value by using a variable that refers to an object value can accessed. Generate a key these two keywords provide Block Scope variables ( and constants ) in JavaScript names an... `` king123 '' } console that refers to an object literal is the way! Var y = new Boolean ( ) ; if you know how to access the we. In this browser for the next time I comment or command using Nodejs, or Static ) to declare object... = > [ 'name ', 'city ' ] 3 min read the JavaScript object.keys ( runner ;... Javascript treats $ and _ as if they were letters of the object or type. Certain value that we want to use a variable to dynamically generate a key in a JavaScript properties. Trickier sometimes, but if you want to find browser for the next I... Beginners ], how to properly handle Node express graceful shutdown other declaration statements (,! Of expression ( e.g list that contains those keys enthusiast, and website in this browser for next! ( array ) on the resulting array to turn it back into object... ( and constants ) in JavaScript, objects penetrate almost every aspect the. One operand ( a unary operator ) javascript use variable as object key a new collection type map! Required to use a variable for a key again you find that you are now able do... Characters are not known at development time the language command line will delete... Be created with figure brackets { … } with an optional list of of., an object must be a Variant, an object key is a of...: keys and values are written in double quotes separated by a colon: command! Var obj = { [ username ]: value } Where key can any!

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