* To use js file in salesforce lightning follow the below steps
Step 1: Upload the JS file in static resources
Step 2: Then call the static resource file u=into lightning by using below tag
   <ltng:require styles="/resource/myResources/styles/styles.css"
                  scripts='/resource/myResources/scripts/js1.js,
                          /resource/myResources/scripts/js2.js'
                  afterScriptsLoaded="{!c.setup}" />
 
styles : if it is custom styles then use styles type in tag.
scripts :  if it is JS file then use scripts type in tag.
afterScriptsLoaded : It is an event which is fired after the script or styles are loaded. After that we can perform any action on it.
/resource/myResources/scripts :  It is the path that the script file is located. You can save as you like.
/js1.js : This the file which we want get it.
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Lightning Web Components



1. new programming model for building Lightning components.
2. Salesforce implementation of that new breed of lightweight frameworks built on web standards.
3. leverages custom elements, templates, shadow DOM, decorators, modules, and other new language constructs available in ECMAScript 7 and beyond.



4. provides a layer of specialized Salesforce services on top of the core stack
a. Base Lightning Components, a set of over 70 UI components all built as custom elements.
b. Lightning Data Service which provides declarative access to Salesforce data and metadata, data caching, and data synchronization.
c. User Interface API, the underlying service that makes Base Lightning Components and the Lightning Data Service metadata aware, leading to substantial productivity gains.
5. there are now two ways to build Lightning components:
a. Aura Components, leveraging its own component model, templates, and modular development programming model.
b. Lightning Web Components, built on top of the web standards breakthroughs of the last five years: web components, custom elements, Shadow DOM, etc.
6. Aura components and Lightning web components can coexist on the same page
7. Aura components can include Lightning web components
8. Aura components and Lightning web components share the same base Lightning components. Base Lightning components were already implemented as Lightning web components.
9. Aura components and Lightning web components share the same underlying services (Lightning Data Service, User Interface API, etc.).

https://developer.salesforce.com/blogs/2018/12/introducing-lightning-web-components.html

Q. Test classes

1. Used for unit testing the code
2. @isTest, testmethod, @testSetup are used
3. TestSetup is for setting the test data for the test class, as a test from one test method is not visible in another
4. Use a data factory for creating test data
5. Use mock responses for testing web services(static resource mock, httpcalloutmock, webservice mock)
6. Use Test.startTest, Test.stopTest to maintain within the limits
7. Using SeeAllData=true will allow the test class to access all the data of org.
8. System.runAs helps in executing a test class in user mode.

Test best practices:

1. If code uses conditional logic (including ternary operators), execute each branch.
2. Make calls to methods using both valid and invalid inputs. (positive and negative testing)
3. Complete successfully without throwing any exceptions, unless those errors are expected and caught in a try…catch block.
4. Always handle all exceptions that are caught, instead of merely catching the exceptions.
5. Use System.assert methods to prove that code behaves properly.
6. Use the runAs method to test your application in different user contexts.
7. Exercise bulk trigger functionality—use at least 20 records in your tests.
8. Use the ORDER BY keywords to ensure that the records are returned in the expected order.
9. Not assume that record IDs are in sequential order.
10. Do not user SeeAllData=true if it is not necessary.

API What you can do with it

1. SOAP API Integrate your org’s data with other applications using standard SOAP protocols.
2. REST API Access objects in your org using standard REST protocols.
3. Metadata API Manage customizations in your org and build tools that manage your metadata model.
4. Tooling API Build custom development tools for platform applications.
5. Marketing Cloud API Expose Marketing Cloud capabilities with the REST API and get comprehensive access to most email functionality with the SOAP API.
6. Bulk API Load, delete, and perform asynchronous queries on large data sets.
7. Streaming API Send and receive notifications securely and efficiently. Notifications can reflect data changes in your org, or custom events.
8. Chatter REST API Build UI for Chatter, Communities, Recommendations, Files, Topics, and more.
9. Mobile SDK While it’s technically a software development kit, it’s worth including here. Integrate Native or Hybrid mobile apps directly with Salesforce.

Opportunity Stages

• Prospecting
• Developing
• Negotiation/Review
• Closed/Won
• Closed/Lost

1. Convert Leads to Opportunities, Accounts, and Contacts
2. When you qualify a lead, you can convert the lead record into an opportunity. You’ll then work your opportunity until you close the deal either by completing it or canceling it.
3. Qualifying a lead indicates that you believe that the lead has a use for and interest in your products, and that a sale to the lead is a definite possibility
4. When you convert a lead, Salesforce uses the information stored in the lead record to create a business account, a contact, and an opportunity.
5. If your organization has person accounts enabled and the lead record didn’t include a company name, the lead is converted into a person account and an opportunity.