Javascript: Predict the value of this argument

this is determined by the calling context, the way in which function is called.

Calling standalone functions directly

When a function is executed as a simple object function directly, this refers to the global object.

function foo() {
   console.log('Hello World!');
   console.log(this);
}

foo();

Calling functions as property of an object reference

Here we have created an object obj, and there is a property on it which is a function. The function is being called as a property on the object. Here this refers to the object obj itself.

var obj = {};

obj.foo = function() {
   console.log('Hello World!');
   console.log(this);
}

obj.foo();

Calling standalone functions using 'new' keyword

When a function is called using the new keyword, this always refer to the newly created object, an empty object.

function foo() {
   console.log('Hello World!');
   console.log(this);
}

new foo();

Javascript: Identifying Primitive and Reference Types

Identifying Primitive Types

There are five primitive types in JavaScript:

• boolean
• number
• string
• null
• undefined

The best way to identify primitive types is with the typeof operator, which works on any variable and returns a string indicating the type of data.

console.log(typeof "John Doe");   // "string"
console.log(typeof 10);           // "number"
console.log(typeof 5.1);          // "number"
console.log(typeof true);         // "boolean"
console.log(typeof undefined);    // "undefined"

When you run typeof null, the result is "object". The best way to determine if a value is null is to compare it against null directly, like below. Make sure that when you’re trying to identify null, use triple equals so that you can correctly identify the type.

console.log(value === null);    // true or false

Identifying Reference Types

The built-in reference types are

• Array
• Date
• Error
• Function
• Object
• RegExp

A function is the easiest reference type to identify because when you use the typeof operator on a function, the operator should return "function":

function reflect(value) {
 return value;
}
console.log(typeof reflect);   // "function"

Other reference types are trickier to identify because, for all reference types other than functions, typeof returns "object". To identify reference types more easily, you can use JavaScript’s instanceof operator. The instanceof operator takes an object and a constructor as parameters. When the value is an instance of the type that the constructor specifies, instanceof returns true; otherwise, it returns false.

var items = [];
var object = {};

function reflect(value) {
 return value;
}
console.log(items instanceof Array);    // true
console.log(object instanceof Object);    // true
console.log(reflect instanceof Function);   // true

Array.isArray() is the best way to identify arrays.

var items = [];
console.log(Array.isArray(items));    // true

Salesforce Lightning Picklist Component

This picklist component is based on SLDS, and the code of this component is heavily borrowed from Caspar Harmer's multi-select component. The component has been customized to suit the basic needs of a simple picklist.

Refer the github link for the code:
https://github.com/iamsonal/Picklist

JavaScript: Module Pattern

The module pattern is an object-creation pattern designed to create singleton objects with private data. The basic approach is to use an immediately invoked function expression (IIFE) that returns an object. An IIFE is a function expression that is defined and then called immediately to produce a result. That function expression can contain any number of local variables that aren’t accessible from outside that function. Because the returned object is defined within that function, the object’s methods have access to the data. Methods that access private data in this way are called privileged methods.

Here’s the basic format for the module pattern. In this pattern, an anonymous function is created and executed immediately. (Note the extra parentheses at the end of the function. You can execute anonymous functions immediately using this syntax.) That means the function exists for just a moment, is executed, and then is destroyed.

var yourObject = (function() {

   // private data variables

   return {
      // public methods and properties
   };

}());

The below code creates the person object using the module pattern. The age variable acts like a private property for the object. It can’t be accessed directly from outside the object, but it can be used by the object methods. There are two privileged methods on the object: getAge(), which reads the value of the age variable, and growOlder(), which increments age. Both of these methods can access the variable age directly because it is defined in the outer function in which they are defined.

var person = (function() {

   var age = 25;

   return {
      name: "Nicholas",

      getAge: function() {
         return age;
      },

      growOlder: function() {
         age++;
      }
   };

}());

console.log(person.name);   // "Nicholas"
console.log(person.getAge());   // 25

person.age = 100;
console.log(person.getAge());   // 25

person.growOlder();
console.log(person.getAge());   // 26

Revealing Module Pattern

There is a variation of the module pattern called the revealing module pattern, which arranges all variables and methods at the top of the IIFE and simply assigns them to the returned object. You can write the previous example using the revealing module pattern as follows:

var person = (function() {

   var age = 25;

   function getAge() {
      return age;
   }

   function growOlder() {
      age++;
   }

   return {
      name: "Nicholas",
      getAge: getAge,
      growOlder: growOlder
   };
   
}());

In this pattern, age, getAge(), and growOlder() are all defined as local to the IIFE. The getAge() and growOlder() functions are then assigned to the returned object, effectively "revealing" them outside the IIFE.

Source: The principles of object-oriented JavaScript by Nicholas

Reference: https://coryrylan.com/blog/javascript-module-pattern-basics

Creating Lightweight Integrations with the Force.com REST API

REST API is simple access to Salesforce data and functionality via RESTful endpoints. It uses resource definition and HTTP verbs in a stateless fashion in order to communicate with the system.

Salesforce uses the OAuth protocol to allow users of applications to securely access data without having to reveal username and password credentials.

Before making REST API calls, you must authenticate the application user using OAuth 2.0. To do so, you’ll need to:

• Set up your application as a connected app (that defines your application’s OAuth settings) in the Salesforce organization. When you develop an external application that needs to authenticate with Salesforce, you need to define it as a new connected app within the Salesforce organization that informs Salesforce of this new authentication entry point.
• Determine the correct Salesforce OAuth endpoint for your connected app to use. OAuth endpoints are the URLs you use to make OAuth authentication requests to Salesforce.
  
  • For authorization: https://login.salesforce.com/services/oauth2/authorize
  • For token requests: https://login.salesforce.com/services/oauth2/token
  • For revoking OAuth tokens: https://login.salesforce.com/services/oauth2/revoke
• Authenticate the connected app user via one of several different OAuth 2.0 authentication flows. An OAuth authentication flow defines a series of steps used to coordinate the authentication process between your application and Salesforce. Supported OAuth flows include:
  
  • Web server flow, where the server can securely protect the consumer secret.
  • User-agent flow, used by applications that cannot securely store the consumer secret.
  • Username-password flow, where the application has direct access to user credentials.

After successfully authenticating the connected app user with Salesforce, you’ll receive an access token which can be used to make authenticated REST API calls.

I have created a connected app "Sample Connected App". I have enabled OAuth Settings and entered a Callback URL. Depending on the OAuth flow, this is typically the URL that a user’s browser is redirected to, with either the authorization code or token, after successful authentication. The scopes under Selected OAuth Scopes refer to permissions given by the user running the connected app.

The Consumer Key and Consumer Secret is created which can be used to authenticate your application.

Click on Manage to see additional settings.

I have selected Relax IP Restrictions under IP Relaxation. Now lets go into Postman. I will be posting values, and for that I have to provide data in payload to get back the token. I will be using form-data as I will be providing a number of values. I have set the grant-type as password because I will be using username-password OAuth authentication flow (which is not ideal in most cases). The value for client_id will be the consumer key.

So this says that we have logged-in. Now lets try to get a list of accounts. Create a new request using the instance URL (INSTANCE_URL/services/data/v41.0/sobjects/account) that we received in the response earlier and for Authorization, concatenate Bearer and the access_token. Click the send button, and you will notice the response.

Similarly, you can check the responses for the below request URL:

INSTANCE_URL/services/data/v41.0/sobjects/account/describe
INSTANCE_URL/services/data/v41.0/sobjects/account/0017F00000I5zDl
INSTANCE_URL/services/data/v41.0/query?q=select+name+from+account

You can append .xml or .json to URI to get back the right representation. This works in most cases. If you are doing searches, it doesn't work in this way; in such cases, add "accept" header. The default is JSON if you are working in REST API. Now lets add Accept header to a standard HTTP header.

You can now remove Accept header and then append .xml to URI to get the same reponse.

Reference:
https://developer.salesforce.com/docs/atlas.en-us.api_rest.meta/api_rest/intro_understanding_authentication.htm
https://www.forcetalks.com/salesforce-topic/how-to-do-salesforce-to-salesforce-integration-using-rest-api/