You can either update an existing value or create a new one on the same object. Objects are mutable datatypes, meaning you can update the values inside an object, but the memory location doesn't change for that same object even though updates occurred. The new syntax looks great to me and will simplify our JS code in the future - so I will be adopting it going forward. optional chaining + nullish coalescingĬonst age = person?.age ? 18 // this is a 2020 feature of JS - links belowĬonst age = person & person.age & || '1-5-1911' // default to 18 if age is falsyĬonst age = person?.age?.dob ? '1-5-1911' // this is a 2020 feature of JS - see links section We can handle defaults utilizing the || and avoid errors using & or optional chaining in conjunction with nullish coalescing.Ĭonst age = person.age || 18 // default to 18 if age is falsy Further, if you try to access a property that's nested within an undefined property, a type error is through.Ĭonst birthDay = // type error - can't access dob of undefined

If you access a property that isn't defined, a value of undefined is returned. I agree with Douglas Crockford here in that this notation creates less readable code, so push for dot notation instead! Both examples are using the created object above to retrieve values from.ĭot notation makes an easily readable access path, but can only be used on property names that are legal non-reserved JS words.Ĭonst firstCompany = panies įor dynamic or illegal JS words, we must use the access type. There are two options for retrieving values from an object. *note: You can use omit the '' in keys when they are legal non-reserved JS word. You can nest arrays, objects, functions, and other expressions within the top object as well! You can optionally have comma-separated key-value pairs within, which makes a very nice flexible map. It's a new variable with a pair of curly braces. Objects can inherit properties from other objects through their prototypes - something we will dive into more deeply later in the article!Ĭreating a new object can be done in different ways - using the object literal syntax is my favorite. They can be nested within each other and since Arrays, Functions, and regular expressions are objects, they too can be contained and mapped efficiently.

They are SO useful for creating collections of data and organizing it throughout a web app. A property value can be any JavaScript value except for undefined.' A property name can be any string, including the empty string. 'An object is a container of properties, where a property has a name and value. 'Objects in JavaScript are mutable keyed collections.' This essential part of the language makes JS special due to the flexibility and quickness one can create data maps, abstractions, and more. Chapter 3 of JavaScript: The Good Parts by Douglas Crockford is all about objects.

Js the good parts