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Code Fellows 201

Day 06 Notes

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JavaScript Object Basics

How would you describe an object to a non-technical friend you grew up with?

• an object is a collection of similar commands an computer program tracks with the same first name. The last name tells the computer which command to run.

What are some advantages to creating object literals?

• It is very common to create an object using an object literal when you want to transfer a series of structured, related data items in some manner, for example sending a request to the server to be put into a database. Sending a single object is much more efficient than sending several items individually, and it is easier to work with than an array, when you want to identify individual items by name.

How do objects differ from arrays?

• objects have properties that can be called using this. or other name(string value)
• arrays cannot have properties that can be called by name, array items are called only by index

Give an example for when you would need to use bracket notation to access an object’s property instead of dot notation.

• Dot notation is generally preferred over bracket notation because it is more succinct and easier to read. However there are some cases where you have to use brackets. For example, if an object property name is defined at runtime then you can’t use dot notation to access the value, but you can pass the name as a variable inside brackets

Evaluate the code below. What does the term this refer to and what is the advantage to using this?

const dog = { name: ‘Spot’, age: 2, color: ‘white with black spots’, humanAge: function (){ console.log(${this.name} is ${this.age*7} in human years); } }

• this is a quick way to tell the computer to staty within the object for property references, instead of looking outside and taking more time and coding effort

Introduction To The DOM

What is the DOM?

• The Document Object Model (DOM) is a programming interface for web documents. It represents the page so that programs can change the document structure, style, and content. The DOM represents the document as nodes and objects; that way, programming languages can interact with the page.

• A web page is a document that can be either displayed in the browser window or as the HTML source. In both cases, it is the same document but the Document Object Model (DOM) representation allows it to be manipulated. As an object-oriented representation of the web page, it can be modified with a scripting language such as JavaScript.

Briefly describe the relationship between the DOM and JavaScript.

• The previous short example, like nearly all examples, is JavaScript. That is to say, it is written in JavaScript, but uses the DOM to access the document and its elements. The DOM is not a programming language, but without it, the JavaScript language wouldn’t have any model or notion of web pages, HTML documents, SVG documents, and their component parts. The document as a whole, the head, tables within the document, table headers, text within the table cells, and all other elements in a document are parts of the document object model for that document. They can all be accessed and manipulated using the DOM and a scripting language like JavaScript.

• The DOM is not part of the JavaScript language, but is instead a Web API used to build websites. JavaScript can also be used in other contexts. For example, Node.js runs JavaScript programs on a computer, but provides a different set of APIs, and the DOM API is not a core part of the Node.js runtime.

• The DOM was designed to be independent of any particular programming language, making the structural representation of the document available from a single, consistent API.

Bookmark and Review

Understanding the problem domain is the hardest part of programming

What’s the difference between primitive values and object references in JavaScript?