Reading-Notes

Class 06 Summary

Problems Domain:

Understanding Problem domain is the hardest part of programming

Hardest things in writing code:

1. Learning new technology
2. Naming things
3. Testing our code
4. Debugging
5. Fixing bugs

To make Programming easy we should understand the problem domain ***********************************

Object In JavaScript:

What is object?

 a set of variables and functions to create a model of something from the real world.

• Properties are variables in an object , and Functios become Methods.
• Properties and Methods have name and value . the name called a key.
• An object cannot have two keys with the same name.

• Property value can be string, number, Boolean, array or another object.but the value of method is always a function.

• Example: var person = { firstName: “John”, lastName: “Doe”, age: 50, eyeColor: “blue” };

• We use dot notation to access object properties and methods. example: let name=person.firstName; or name = person[‘firstname’];

Document Object Model(DOM):

Making The HTML Model and With the HTML DOM,JavaScript can access and change all the elements of an HTML document.

• The DOM tree is a model of a web page.it consists of 4 types of nodes:
  1. The document node.
  2. Element nodes.
  3. Attribute nodes.
  4. Text Nodes

• DOM Queries: methods to find elements in the DOM tree .

• Storing elements in variables = storing the location of the elements in DOM tree. Example : var itemOne = getElementById(‘one’);

DOM queries return one element, or return a Nodelist, which is a collection of nodes.

• Methods return a single element node:
  1. getElementById(‘id’)
  2. querySelector(‘css selector’)
• Methods return nodeList:
  1. getElementByClassName(‘class’)
  2. getElementByTagName(‘tagname’)
  3. querySelectorAll(‘css selector’)
• If we have a nodeList we can loop through each node and do statement to each.

Example: var myNodelist = document.querySelectorAll(“p”); var i; for (i = 0; i < myNodelist.length; i++) { myNodelist[i].style.color = “red”; }