Javascript: Arrow functions and this

Arrow functions are anonymous; there are only arrow function expressions. You can assign arrow function expression to a variable, can be used in an IIFE as well as a callback function. Below you will find valid arrow functions:

(a, b) => a + b // implicitly returning a + b

(a, b) => {                // explicitly returning a + b
   return a + b;
}

a => a * a                // omit () when there is one parameter

() => 2                   // () mandatory when there are no parameters

(a, b) => {               // explicitly returning JS object
   return {
      a1: a, b1: b
   }
}

(a, b) => ({              // implicitly returning JS object
   a1: a, b1: b
})

An arrow function does not have its own this. this in arrow functions is always statically defined by the surrounding lexical scope.

In the example below, when using traditional function, this refers to the num object, whereas when using arrow notation, this is pointing to the global object. Arrow functions doesn't have its own this, and so this refers to outer scope, and outer scope for num object is the window object.

Even if I use call() method, result is the same.

In the below example, when using traditional function, this refers to the global object, whereas using arrow function, we get the desired result.

In order to get the greeting message using the traditional function, there are several ways to keep reference to this object inside of setTimeOut function. You can create a self variable like below:

const str = {
    value: 'Delayed greeting',
    greet: function() {
        const self = this;
        setTimeout(function() {
            console.log(self.value);
        }, 2000)
    }
};

str.greet();

or bind with this like below:

const str = {
    value: "Delayed greeting",
    greet: function() {
        setTimeout(
            function() {
                console.log(this.value);
            }.bind(this),
            2000
        );
    }
};

str.greet();

It is not possible to use arrow function expression as a function constructor and create new objects from it.

LWC: Fetch picklist values

<!-- fetchPicklistValues.html -->
<template>
    <lightning-card title="WireGetPicklistValues" icon-name="custom:custom67">
        <template if:true={picklistValues.data}>
            <div class="slds-m-around_medium">
                <template for:each={picklistValues.data.values} for:item="item">
                    <lightning-input
                        key={item.value}
                        label={item.label}
                        data-value={item.value}
                        type="checkbox"
                        onchange={handleCheckboxChange}
                    ></lightning-input>
                </template>
            </div>
        </template>
    </lightning-card>
</template>

// fetchPicklistValues.js
import { LightningElement, wire } from 'lwc';
import { getPicklistValues } from 'lightning/uiObjectInfoApi';
import TYPE_FIELD from '@salesforce/schema/Account.Type';

import { getObjectInfo } from 'lightning/uiObjectInfoApi';
import ACCOUNT_OBJECT from '@salesforce/schema/Account';

export default class FetchPicklistValues extends LightningElement {

    @wire(getObjectInfo, { objectApiName: ACCOUNT_OBJECT })
    objectInfo;

    @wire(getPicklistValues, {
        recordTypeId: '$objectInfo.data.defaultRecordTypeId',
        fieldApiName: TYPE_FIELD
    })
    picklistValues;

    handleCheckboxChange(event) {
        console.log(event.target.dataset.value);
        console.log(event.target.checked);
    }
}

As per documentation, use getPicklistValues wire adapter (from lightning/uiObjectInfoApi module) to fetch picklist values for a specified field.

Parameters:

• recordTypeId—(Required) The ID of the record type. Use the Object Info defaultRecordTypeId property, which is returned from getObjectInfo or getRecordUi.
• fieldApiName—(Required) The API name of the picklist field on a supported object.
• propertyOrFunction—A private property or function that receives the stream of data from the wire service. If a property is decorated with @wire, the results are returned to the property’s data property or error property. If a function is decorated with  @wire, the results are returned in an object with a data property and an error property.

Find out more about the data inside objectInfo and picklistValues variable:

Lightning Web Components: A Tale of Two DOM's

The shadow DOM is a subtree that branches off the DOM (light DOM). It hides away the complexity of components from the rest of the page. It has actually been around for quite a while. In fact, all of these elements utilize the shadow DOM to hide their complex markup and styling away.

<input type="range" />
<video controls width="250"></video>
<input type="date" />

Because of the new concept of shadow DOM, we need to avoid the confusion between the DOM you knew before and this new shadow DOM. So you are going to see the term light DOM used to describe the DOM you have been familiar with and working with all these years. But before we dive into the shadow DOM, here's one more term, the logical DOM. So the logical DOM is an umbrella term, so the light DOM and shadow DOM together are a part of logical DOM.

To understand shadow DOM, let’s look at the HTML5 <video> element, which is a custom element with a shadow DOM. Because Show user agent shadow DOM is enabled in Chrome Developer Tools, you see the #shadow-root node and its child elements, which make up the shadow DOM. If you disable this option, you would see only the <video> tag, and none of its children.

There are a variety of terms that we need to understand when working with the shadow DOM.

• Shadow Host: It is the element in the light DOM that is hosting the shadow DOM. So the shadow host, in this case, is the video tag, and it hosts the shadow root.
• Shadow Root: It is labelled in Chrome dev tools with #shadow-root, and is the root node of the shadow tree, encapsulating a DOM subtree. All this markup within the shadow root is shadow DOM. You can also see a nested shadow tree here, which is also known as a DOM subtree. So one DOM subtree can end up hosting another DOM subtree
• Shadow Boundary: It encapsulates styling rules that are defined within a given piece of shadow DOM. So in other words, a CSS selector that's applied in the shadow DOM doesn't apply to other elements outside of shadow DOM and vice versa. This is because styles in the shadow DOM do not cross over the shadow boundary. The shadow boundary exists at the shadow root. To clarify, the shadow boundary is a concept and is merely a term used to describe the boundary between the light DOM and shadow DOM.

Creating shadow DOM is a simple 3-step process.

1. Select shadow host, which is an element in the light DOM that will wrap the shadow root.
2. Create a shadow root
3. Add elements to the shadow DOM using the same methods that you use to append elements to the light DOM: innerHTML and appendChild

In the code below, the style is only going to impact the light DOM.

<!DOCTYPE html>
<html lang="en">
<head>
    <style>
        h1 { color: red; }
    </style>
</head>
<body>
    <h1>Hello World from the light DOM</h1> 
    <div id="host"></div>

    <template>
        <h1>Hello World from the shadow DOM</h1>
    </template>

    <script>
        var template = document.querySelector('template');
        var host = document.getElementById('host');
        var root = host.attachShadow({mode: 'open'});
        root.appendChild(document.importNode(template.content, true));

        // Only going to get a reference to the light DOM
        console.log(document.querySelectorAll('h1'));

        // Only going to get a reference to the shadow DOM. For multiple pieces of shadow DOM in the page,
        // you need to get the shadow root that is appropriate for the element that you are trying to target
        console.log(root.querySelectorAll('h1'));
    </script>
</body>
</html>

Lightning Web Components

The shadow DOM for a Lightning web component is created automatically. The component author doesn’t have to implement it (no need to use the attachShadow() or appendChild() methods). Also since Lightning web components don’t use the native shadow DOM yet, you can’t view their shadow DOM in Chrome Developer Tools. Even if you enable Show user agent shadow DOM, you don’t see the shadow DOM.

Resources:
https://medium.com/front-end-weekly/the-rise-of-shadow-dom-84aa1f731e82

Salesforce Apex: Regular Expressions

Assume that you receive an email, and your task is to extract all the URLs present in the email body. Copy and paste is a tedious job, right? Using regex script, you can save yourself from the manual work.

You can refer the following code to extract all the URLs from an incoming email.

global class CreateTaskEmailExample implements Messaging.InboundEmailHandler {

  public static final String REGEX_URL = '(?i)\\b((?:[a-z][\\w-]+:(?:/{1,3}|[a-z0-9%])|www\\d{0,3}[.]|[a-z0-9.\\-]+[.][a-z]{2,4}/)(?:[^\\s()<>]+|\\(([^\\s()<>]+|(\\([^\\s()<>]+\\)))*\\))+(?:\\(([^\\s()<>]+|(\\([^\\s()<>]+\\)))*\\)|[^\\s`!()\\[\\]{};:\'".,<>?«»“”‘’]))';
 
  global Messaging.InboundEmailResult handleInboundEmail(Messaging.inboundEmail email, Messaging.InboundEnvelope env){
 
    Messaging.InboundEmailResult result = new Messaging.InboundEmailResult();
    String plainTextBody = email.plainTextBody;

    Matcher m = Pattern.compile(REGEX_URL).matcher(plainTextBody);
    while (m.find()) {
      System.debug(m.group());
    }
    ...
    ...
    ...
    
   }
}

Similarly you can use the following regex expression for email addresses:

String REGEX_EMAIL = '(?:[a-z0-9!#$%&\'*+/=?^_`{|}~-]+(?:\\.[a-z0-9!#$%&\'*+/=?^_`{|}~-]+)*|"(?:[\\x01-\\x08\\x0b\\x0c\\x0e-\\x1f\\x21\\x23-\\x5b\\x5d-\\x7f]|\\\\[\\x01-\\x09\\x0b\\x0c\\x0e-\\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\\x01-\\x08\\x0b\\x0c\\x0e-\\x1f\\x21-\\x5a\\x53-\\x7f]|\\\\[\\x01-\\x09\\x0b\\x0c\\x0e-\\x7f])+)\\])';

and this one for phone numbers

String REGEX_PHONE = '(?:(?:\\+?([1-9]|[0-9][0-9]|[0-9][0-9][0-9])\\s*(?:[.-]\\s*)?)?(?:\\(\\s*([2-9]1[02-9]|[2-9][02-8]1|[2-9][02-8][02-9])\\s*\\)|([0-9][1-9]|[0-9]1[02-9]|[2-9][02-8]1|[2-9][02-8][02-9]))\\s*(?:[.-]\\s*)?)?([2-9]1[02-9]|[2-9][02-9]1|[2-9][02-9]{2})\\s*(?:[.-]\\s*)?([0-9]{4})(?:\\s*(?:#|x\\.?|ext\\.?|extension)\\s*(\\d+))?';

Javascript: Preventing Object Modification

All objects you create are extensible by default, meaning new properties can be added to the object at any time. By setting Extensible attribute on an object to false, you can prevent new properties from being added to an object. There are three different ways to accomplish this.

Preventing Extensions

One way to create a nonextensible object is with Object.preventExtensions(). In the code below, as person1 is nonextensible, the sayName() method is never added to it.

var person1 = {
   name: "Nicholas"
};

console.log(Object.isExtensible(person1));  // true

Object.preventExtensions(person1);
console.log(Object.isExtensible(person1));  // false

person1.sayName = function() {
   console.log(this.name);
};

console.log("sayName" in person1);   // false

Sealing Objects

You can use the Object.seal() method on an object to seal it. A sealed object is nonextensible, and all of its properties are nonconfigurable. That means not only can you not add new properties to the object, but you also can’t remove properties or change their type.

var person1 = {
   name: "Nicholas"
};

console.log(Object.isExtensible(person1));  // true
console.log(Object.isSealed(person1));   // false

Object.seal(person1);
console.log(Object.isExtensible(person1));  // false
console.log(Object.isSealed(person1));   // true

person1.sayName = function() {
   console.log(this.name);
};

console.log("sayName" in person1);   // false

person1.name = "Greg";
console.log(person1.name);    // "Greg"

delete person1.name;
console.log("name" in person1);   // true
console.log(person1.name);    // "Greg"

var descriptor = Object.getOwnPropertyDescriptor(person1, "name");
console.log(descriptor.configurable);   // false

Freezing Objects

If an object is frozen, you can’t add or remove properties, you can’t change properties’ types, and you can’t write to any data properties. In essence, a frozen object is a sealed object where data properties are also read-only. Frozen objects can’t become unfrozen, so they remain in the state they were in when they became frozen.

var person1 = {
   name: "Nicholas"
};
console.log(Object.isExtensible(person1));  // true
console.log(Object.isSealed(person1));   // false
console.log(Object.isFrozen(person1));   // false

Object.freeze(person1);
console.log(Object.isExtensible(person1));  // false
console.log(Object.isSealed(person1));   // true
console.log(Object.isFrozen(person1));   // true

person1.sayName = function() {
   console.log(this.name);
};

console.log("sayName" in person1);   // false

person1.name = "Greg";
console.log(person1.name);    // "Nicholas"

delete person1.name;
console.log("name" in person1);   // true
console.log(person1.name);    // "Nicholas"

var descriptor = Object.getOwnPropertyDescriptor(person1, "name");
console.log(descriptor.configurable);   // false
console.log(descriptor.writable);   // false