The Question : 722 people think this question is useful I am checking for the existence of an object property with a variable holding the property name in question. This is undefined because it’s looking for myObj.myProp but I want it to check for myObj.prop The Question Comments : Possibly useful: From a comment by […] Unlike many object-oriented languages, there is no distinction between a function definition and a method definition in object-related JavaScript. In this post I look at JavaScript object iteration and picking out values from a JavaScript object by property name or index. It's typical when speaking of an object's properties to make a distinction between properties and methods. 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. If it does not match, then it receives an undefined value. 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). identifier is the name of the property to access, aliasIdentifier is the variable name, and expression should evaluate to an object. { name, age } By simply replacing name: name with name, JavaScript understands that you want to take the value name and assign it to a property with the same name as the variable. 0 / 160. brightness_4 The use-case of making a property from a variable is so common, that there’s a special property value shorthand to make it shorter. If it finds one, it assigns the property the value of the variable. A string is passed as a parameter to eval(). You can also combine both regular properties and shorthands in the same object. Inside of the curly braces, properties and their values are specified as a list of key/value pairs. In a function definition, this refers to the "owner" of the function. How to add a property to a JavaScript object using a variable as the name? acknowledge that you have read and understood our, GATE CS Original Papers and Official Keys, ISRO CS Original Papers and Official Keys, ISRO CS Syllabus for Scientist/Engineer Exam. The following example creates an empty object with no properties. The this Keyword. In the example above, this is the person object that "owns" the fullName function. By using our site, you Use cases for Object.getOwnPropertyDescriptors() # Object.getOwnPropertyDescriptors(): copying properties into an object # Since ES6, JavaScript already has had a tool method for copying properties: Object.assign(). JSON is a very powerful and lightweight notation, the only way to use it properly, though is to have a good foundation in what a JavaScript object literal and a JavaScript … map, dictionary, hash, lookup table). In the above example, we use the property name as a string inside square brackets to get the value corresponding to that property name. Below example illustrate explain two different approaches: Example 1: … The list of key/value pairs is comma delimited, with each key and value separated by a colon. I downloaded some JSON which I've converted into an object. We can add the property to JavaScript object using a variable as the name by using dot notation or bracket notation. generate link and share the link here. Reply. For example here, I already used twitter as a variable. How do you run JavaScript script through the Terminal? The name: values pairs in JavaScript objects are called properties. Once an object is created, you can assign property values and invoke methods just like any other object. Strict mode changes previously accepted "bad syntax" into real errors. You can use this equivalent syntax: obj[name] = value 2018-06-27 16:37. 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