To add a new property to an object, specify the object name followed by: a dot, the name of the new property, an equals sign, and the value for the new property (enclosed in quotes if it is a string). They are. JavaScript Properties. Finally, return the created object. In JavaScript, I’ve created an object like so: var data = { 'PropertyA': 1, 'PropertyB': 2, 'PropertyC': 3 }; Is it possible to add further properties to this object after it’s initial creation if the properties name is not determined until run time? Otherwise, add a property with the specified value to the object. Ask Question Asked 5 years, 3 months ago. As you can see from the example above, this syntax makes adding dynamic properties a two-step process. A JavaScript object is a collection of unordered properties. This example is similar to the above example, but the UNKNOWN method attaches a getter/setter pair of methods for the name triggering the UNKNOWN call. Alternatively, if you prefer the Underscore library, you can use _.extendOwn (Alias: _.assign) or _.defaults method. Live Demo i.e. First, you have to create an object, and then only you can add the dynamic property to it. Both Underscore and Lodash libraries offers several utility methods to add properties to an existing object.. With the Lodash library, you can use any of the _.merge, _.assignIn (alias _.extend), _.assign, or _.defaults method. dynamicvar~new d~foo = 123 say d~foo d = . The process for modifying a property is essentially the same. 1) Object.assign() The Object.assign() method is used to copy the values of all properties from one or more source objects to a target object. The new object is created normally, the only difference being is that the dynamic key value is to be put between square brackets [ ]. To dynamically add a property and that it is used by all clones derived from the same object, even if they are created before the property is added, use the reserved word prototype . There are two methods to merge properties of javascript objects dynamically. When the property name is dynamic or is not a valid identifier, a better alternative is square brackets property accessor: object[propertyName]. Given the example in the jsFiddle (updated here), this would produce the following structure: JavaScript provides a bunch of good ways to access object properties. Underscore/Lodash Library. On all subsequent calls, the attribute methods will get called. Sometimes we want to add dynamic properties to an object in JavaScript. Sometimes the property name needs to be stored into a variable. An object may be redefined dynamically with the prototype property You can add a property directly to an already defined object. Dynamically create Javascript Object. 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