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Hello Trailblazers,

In this post we'll understand different lifecycle hooks of lightning web components.

What is a Lifecycle Hook?

What are the different lifecycle hooks of lightning web components?

constructor()

child.js

import { LightningElement, api } from 'lwc';

export default class Child extends LightningElement {

    count = 0;
    @api
    message = 'default';

    constructor() {
        super();
        console.log('Child constructor called');
        console.log(this.count);
        console.log(this.message);
        console.log(this.template.querySelector('lightning-button'));
    }
}

child.html

<template>
    <lightning-button label="Increase Count" onclick={increaseCount}></lightning-button>
    <br /><br />
</template>

connectedCallback()

child.js

import { LightningElement, api } from 'lwc';

export default class Child extends LightningElement {

    count = 0;
    @api
    message = 'default';

    constructor() {
        super();
        console.log('Child constructor called');
        console.log(this.count);
        console.log(this.message);
        console.log(this.template.querySelector('lightning-button'));
    }

    connectedCallback() {
        console.log('Child connected callback called');
        console.log(this.count);
        console.log(this.message);
        console.log(this.template.querySelector('lightning-button'));
    }
}

parent.html

<template>
    <c-child message="hello"></c-child>
</template>

parent.js

import { LightningElement } from 'lwc';

export default class Parent extends LightningElement {

    constructor() {
        super();
        console.log('Parent constructor called');
    }

    connectedCallback() {
        console.log('Parent connected callback called');
        console.log(this.template.querySelector('c-child'));
    }

    renderedCallback() {
        console.log('Parent rendered callback called');
        console.log(this.template.querySelector('c-child'));
    }
}

1. Parent constructor() is called
   
   
2. Parent connectedCallback() is called and the reference to child component c-child is coming as null inside it
   
   
3. Child constructor() is called. Value of count is 0, message is undefined and reference to lightning-button is coming as null as it's further a child component for our child lwc.
   
   
4. Child connectedCallback() is called where value of count is 0. Notice that the value of message is hello instead of default this time because this is the value which is passed from our parent lwc to child lwc for this public property, reference to lightning-button is still coming as null
   
   
5. Finally, our renderedCallback() method is called in our parent component as per the order and as it's called after the child's connectedCallback() method, this means that the child lwc is now connected to the DOM. Therefore, reference to child lwc is not coming as null this time, as it was coming in the parent's connectedCallback() method.

I hope all of this is clear. Now, let's move on to the renderedCallback() method.

renderedCallback()

As the name suggests, this callback method is called once the component has rendered. As the component can render multiple times, this callback method will also be called each time the component is re-rendered. Some important points about renderedCallback() are:

1. renderedCallback() on the child component is called before it's called on the parent component
   
   
2. Whenever the component renders, the expressions used in a template are re-evaluated. This means that if we've created a getter method which is used in our html file and that getter is returning a dynamic value based on some properties, it'll be re-evaluated as well
   
   
3. Whenever the component's state is changed, the component will be re-rendered
   
   
4. When a component is re-rendered, the lwc engine attempts to reuse the existing elements. For example: if you update something in the parent component due to which the parent re-renders, it'll not re-render the child component. Another example can be: if you're displaying a list of child components and if you re-order the list, then although the components are placed at different positions now, they're not re-rendered. The engine assumes that the same components are being used and just placed at a different positions now, so they're not re-rendered
   
   However, if you use a different key/update the key of child component, it might get re-rendered - I'm not going to show a demo of this, this is your homework. Try and let me know how it works in the comments down below!
   
   
5. As I specified in point 3, whenever the component's state is changed, the component will be re-rendered. Therefore, we need to make sure that we don't update the state of the component (for example: a property which is being displayed in component's html) in the renderedCallback() itself as it'll re-render the component and will call renderedCallback() again. In this case, the renderedCallback() will be called again and again recursively which will result in an infinite loop
   

We've already defined renderedCallback() in our parent component as specified in the connectedCallback() section. Let's define renderedCallback() in our child lwc as well.

child.js

import { LightningElement, api } from 'lwc';

export default class Child extends LightningElement {

    count = 0;
    @api
    message = 'default';

    constructor() {
        super();
        console.log('Child constructor called');
        console.log(this.count);
        console.log(this.message);
        console.log(this.template.querySelector('lightning-button'));
    }

    connectedCallback() {
        console.log('Child connected callback called');
        console.log(this.count);
        console.log(this.message);
        console.log(this.template.querySelector('lightning-button'));
    }

    renderedCallback() {
        console.log('Child rendered callback called');
        console.log(this.template.querySelector('lightning-button'));
    }
}

Let's have a look at the updated logs now:

The order  of events is provided below:

1. Parent constructor called
   
   
2. Parent connected callback called where reference to child lwc is coming as null
   
   
3. Child constructor called where count is 0, message is undefined and reference to lightning-button is coming as null
   
   
4. Child connected callback called where count is 0, message is hello and reference to lightning-button is again coming as null
   
   
5. Child rendered callback called where reference to lightning-button is coming properly as the lightning-button is connected to the DOM now
   
   
6. At last, parent rendered callback is called where reference to child lwc is coming properly as the child lwc is connected to DOM now

We are now going to re-render the parent lwc to see when renderedcallback() is called in parent and child LWCs. Let's add some more code!

If you remember, our child lwc html is calling a method increaseCount() when the lightning-button is clicked, let's add that method to our child lwc js file as shown below:

increaseCount() {
    this.dispatchEvent(new CustomEvent('increasecount', {
        detail: {
            message: 'Increased count to ' + (++this.count)
        }
    }));
}

This method will fire an event named increasecount whenever the button is clicked which will contain a message with the value of count variable increased by 1. The full code of child.js is provided below:

child.js

import { LightningElement, api } from 'lwc';

export default class Child extends LightningElement {

    count = 0;
    @api
    message = 'default';

    constructor() {
        super();
        console.log('Child constructor called');
        console.log(this.count);
        console.log(this.message);
        console.log(this.template.querySelector('lightning-button'));
    }

    connectedCallback() {
        console.log('Child connected callback called');
        console.log(this.count);
        console.log(this.message);
        console.log(this.template.querySelector('lightning-button'));
    }

    renderedCallback() {
        console.log('Child rendered callback called');
        console.log(this.template.querySelector('lightning-button'));
    }

    increaseCount() {
        this.dispatchEvent(new CustomEvent('increasecount', {
            detail: {
                message: 'Increased count to ' + (++this.count)
            }
        }));
    }
}

Notice the increaseCount() added at the end. Let's update our parent.html file as well now:

parent.html

<template>
    <lightning-card title={message}>
        <p class="slds-var-p-around_small">
            <c-child onincreasecount={updateMessage} message="hello"></c-child>
        </p>
    </lightning-card>
</template>

As you can see above, I've covered my child lwc with a lightning card which is displaying the value of message variable as title. I'm also capturing the increasecount event and calling another method in my parent.js named updateMessage() which will update the value of message variable displayed in the card title. Finally, let's take a look at our updateMessage() defined in parent.js as well:

updateMessage(event) {
    this.message = event.detail.message;
}

As you can see above, it's updating the message variable with the value of message coming from the event. This message variable will be displayed as the title of lightning-card. Let's have a look at the full code below:

parent.js

import { LightningElement, track } from 'lwc';

export default class Parent extends LightningElement {

    message = 'Updated count will appear here!';

    constructor() {
        super();
        console.log('Parent constructor called');
    }

    connectedCallback() {
        console.log('Parent connected callback called');
        console.log(this.template.querySelector('c-child'));
    }

    renderedCallback() {
        console.log('Parent rendered callback called');
        console.log(this.template.querySelector('c-child'));
    }

    updateMessage(event) {
        this.message = event.detail.message;
    }
}

Notice the default value of message variable as: Updated count will appear here!. I've defined the updateMessage() method at the end which is updating the value of this message variable. Let's take a look at the component in action:

As we click the Increase Count button present in child lwc, it fires an event with updated value of count. This increasecount event is captured by parent lwc and it'll update the value of message variable shown as a title of lightning-card as shown above.

The thing to notice here is that, each time we click the button and the event is fired, it re-renders the parent component as shown below:

Notice that only the parent lwc's rendered callback is called again and again and not the child one as I increased count from 1 to 5. This means that even though the parent is rendered multiple times, the child LWC is just reused as there's no change in the state of child lwc. It's still showing the same Increase Count button. This covers our point 3 and 4  under important points about renderedCallback(). It's time to move on to the next callback method now i.e. disconnectedCallback()

disconnectedCallback()

disconnectedCallback() will be called whenever the component is disconnected from the DOM, it's mainly useful to clean up the work done in connectedCallback(). You can use it for simple purposes like to remove cache or event listeners. Let's define disconnectedCallback() on our child component js. You can simply add the below method:

disconnectedCallback() {
    console.log('Child disconnected callback called');
}

Our updated child.js file is shown below:

child.js

import { LightningElement, api } from 'lwc';

export default class Child extends LightningElement {

    count = 0;
    @api
    message = 'default';

    constructor() {
        super();
        console.log('Child constructor called');
        console.log(this.count);
        console.log(this.message);
        console.log(this.template.querySelector('lightning-button'));
    }

    connectedCallback() {
        console.log('Child connected callback called');
        console.log(this.count);
        console.log(this.message);
        console.log(this.template.querySelector('lightning-button'));
    }

    renderedCallback() {
        console.log('Child rendered callback called');
        console.log(this.template.querySelector('lightning-button'));
    }

    disconnectedCallback() {
        console.log('Child disconnected callback called');
    }

    increaseCount() {
        this.dispatchEvent(new CustomEvent('increasecount', {
            detail: {
                message: 'Increased count to ' + (++this.count)
            }
        }));
    }
}

Notice the disconnectedCallback() added above the increaseCount() and below renderedCallback(). Let's update our parent component a little bit as well to make sure we're able to disconnect child lwc from the DOM.

Updated parent.html file is provided below:

parent.html

<template>
    <lightning-card title={message}>
        <p class="slds-var-p-around_small">
            <template if:true={show}>
                <c-child onincreasecount={updateMessage} message="hello"></c-child>
            </template>
            <lightning-button label="Toggle Child" onclick={toggleChild}></lightning-button>
        </p>
    </lightning-card>
</template>

As you can see above, I've added a template tag with if:true condition which is checking a boolean variable named show. Only when this variable is true, our child component will be displayed to us. I'm going to create this variable in our parent.js file. I've added another lightning-button with label Toggle Child which is calling the toggleChild() when clicked. On click of this button, I'm going to toggle the value of show variable from true -> false or from false -> true which will hide/show the child lwc component. This will utlimately call our disconnectedCallback() on our child lwc as well. Let's take a look at the updated parent.js now:

parent.js

import { LightningElement, track } from 'lwc';

export default class Parent extends LightningElement {

    message = 'Updated count will appear here!';
    show = true;

    constructor() {
        super();
        console.log('Parent constructor called');
    }

    connectedCallback() {
        console.log('Parent connected callback called');
        console.log(this.template.querySelector('c-child'));
    }

    renderedCallback() {
        console.log('Parent rendered callback called');
        console.log(this.template.querySelector('c-child'));
    }

    updateMessage(event) {
        this.message = event.detail.message;
    }

    toggleChild() {
        this.show = !this.show;
    }
}

As you can see above, I've added show variable below message variable whose default value is true. I've also added another method named toggleChild() at the end. This method will be called when we click the Toggle Child lightning button and it'll toggle the value of show variable from true to false and from false to true.

This toggling will automatically hide/show the child lwc or I can say connect/disconnect child lwc from the DOM. Let's take a look at the component in action first:

As you can see in the above demo, first of all I increased the count using Increase Count lightning-button in the child component to 2. Then I clicked on Toggle Child button which removed the child component from the DOM. I brought it back by clicking the Toggle Child button again and then I clicked on Increase Count button again which increased the value of count starting from 1 to 5. It started from 1 again as the child lwc is reinitialized and therefore is having the default value of count as 0. Let's take a look at related logs now.

After the components were loaded initially and I clicked on Increase Count button twice and then the Toggle Child button which removed the child lwc from DOM. The console.log statements for these 3 operations are shown below:

As you can see, for the first two operations, when count is increased, parent renderedCallback() is called and I can refer the child lwc easily as it's connected to the DOM. Then I clicked Toggle Child button, it called child's disconnectedCallback() and we have the statement: Child disconnected callback called printed to the console. It also called parent's renderedCallback() as the child is removed from the DOM so the parent is also re-rendered. Notice that this time, the child lwc reference in the parent's renderedCallback() is coming as null as the child component is no more connected to the DOM.

Let's click the Toggle Child button again now:

As you can see above, as I clicked on Toggle Child button again, the child lwc is again connected to DOM. Therefore, the child constructor() is called again, then child connectedCallback() is called, then renderedCallback() and finally parent's renderedCallback() is called once again and this time the reference to child lwc is not coming as null.

Post that, I clicked on Increase Count button 5 more times, the count is increased from 1 to 5 and the parent lwc is rendered 5 times as shown below:

errorCallback()

Now, let's take a look at our last method in the lwc lifecycle i.e. errorCallback(). This callback method will be called whenever an error occurs in lifecycle hook and it captures errors in all the child (descendent) components in it's tree. Let's understand with an example. I'm going to throw error from the connectedCallback() of my child.js file. I'll also define errorCallback() methods in both child and parent lwc to understand which method is being called and the information received in the errorCallback() method. Let's update our child lwc first.

child.js

import { LightningElement, api } from 'lwc';

export default class Child extends LightningElement {

    count = 0;
    @api
    message = 'default';

    constructor() {
        super();
        console.log('Child constructor called');
        console.log(this.count);
        console.log(this.message);
        console.log(this.template.querySelector('lightning-button'));
    }

    connectedCallback() {
        console.log('Child connected callback called');
        console.log(this.count);
        console.log(this.message);
        console.log(this.template.querySelector('lightning-button'));
        let error = {
            code: 100,
            message: 'Error from child connected callback!'
        };
        throw error;
    }

    renderedCallback() {
        console.log('Child rendered callback called');
        console.log(this.template.querySelector('lightning-button'));
    }

    disconnectedCallback() {
        console.log('Child disconnected callback called');
    }

    errorCallback(error, stack) {
        console.log('Child error callback called, error = ' + JSON.stringify(error) + ', stack = ' + JSON.stringify(stack));
    }

    increaseCount() {
        this.dispatchEvent(new CustomEvent('increasecount', {
            detail: {
                message: 'Increased count to ' + (++this.count)
            }
        }));
    }
}

connectedCallback() {
    console.log('Child connected callback called');
    console.log(this.count);
    console.log(this.message);
    console.log(this.template.querySelector('lightning-button'));
    let error = {
        code: 100,
        message: 'Error from child connected callback!'
    };
    throw error;
}

errorCallback(error, stack) {
    console.log('Child error callback called, error = ' + JSON.stringify(error) + ', stack = ' + JSON.stringify(stack));
}

errorCallback(error, stack) {
    console.log('Parent error callback called, error = ' + JSON.stringify(error) + ', stack = ' + stack);
    console.log(this.template.querySelector('c-child'));
}

parent.js

import { LightningElement, track } from 'lwc';

export default class Parent extends LightningElement {

    message = 'Updated count will appear here!';
    show = true;

    constructor() {
        super();
        console.log('Parent constructor called');
    }

    connectedCallback() {
        console.log('Parent connected callback called');
        console.log(this.template.querySelector('c-child'));
    }

    renderedCallback() {
        console.log('Parent rendered callback called');
        console.log(this.template.querySelector('c-child'));
    }

    errorCallback(error, stack) {
        console.log('Parent error callback called, error = ' + JSON.stringify(error) + ', stack = ' + stack);
        console.log(this.template.querySelector('c-child'));
    }

    updateMessage(event) {
        this.message = event.detail.message;
    }

    toggleChild() {
        this.show = !this.show;
    }
}

What is an Event-Driven Software Architecture?

Why and When should I use platform events?

Types of Platform Events

Standard Platform Events

Custom Platform Events

Publishing Platform Events

That's all for this tutorial. I hope you liked it, let me know your feedback in the comments down below. You can connect with my on Connections app by scanning the QR code given below:

Or search in the code scanner screen using my username: rahulmalhotra

Happy Trailblazing!!

The Problem

SELECT Subject, Owner.FederationIdentifier FROM Case WHERE Id = '5005D000008nxIkQAI'

SELECT Subject, Owner.FederationIdentifier FROM
                ^
ERROR at Row:1:Column:17
No such column 'FederationIdentifier' on entity 'Name'. If you are attempting to use a custom field, be sure to append the '__c' after the custom field name. Please reference your WSDL or the describe call for the appropriate names.

The Solution

SELECT Id, TYPEOF Owner WHEN User Then FederationIdentifier END FROM Case WHERE Id = '5005D000008nxIkQAI' AND Owner.Type = 'User'

Starting SFDX: Execute SOQL Query...

07:30:06.358 sfdx force:data:soql:query --query SELECT Id, TYPEOF Owner WHEN User Then FederationIdentifier END FROM Case WHERE Id = '5005D000008nxIkQAI' AND Owner.Type = 'User'
Querying Data... done
 ID                 OWNER                                                              
 ────────────────── ────────────────────────────────────────────────────────────────── 
 5005D000008nxIkQAI {                                                                  
                      "attributes": {                                                  
                        "type": "User",                                                
                        "url": "/services/data/v56.0/sobjects/User/0055D000005BiagQAC" 
                      },                                                               
                      "FederationIdentifier": "12345"                                  
                    }                                                                  
Total number of records retrieved: 1.
07:30:10.900 sfdx force:data:soql:query --query SELECT Id, TYPEOF Owner WHEN User Then FederationIdentifier END FROM Case WHERE Id = '5005D000008nxIkQAI' AND Owner.Type = 'User'
 ended with exit code 0

List<Case> caseList = [SELECT Id, TYPEOF Owner WHEN User Then FederationIdentifier END FROM Case WHERE Id = '5005D000008nxIkQAI' AND Owner.Type = 'User'];
User caseOwner = caseList[0].Owner;
System.debug(caseOwner.FederationIdentifier);

Task linked to account

Task linked to opportunity

Task linked to case

Task linked to product

List<Task> taskList = [SELECT Subject, 
    TYPEOF What 
    	WHEN Account THEN Type, NumberOfEmployees 
    	WHEN Opportunity THEN Amount, CloseDate 
    	WHEN Case THEN Subject, CaseNumber 
    	ELSE Name 
    END 
FROM Task];
for(Task taskRecord: taskList) {
    System.debug(taskRecord.Subject + ' -> ' + taskRecord.What);
}

If you remember, in our initial query on Case (SELECT Id, TYPEOF Owner WHEN User Then FederationIdentifier END FROM Case WHERE Id = '5005D000008nxIkQAI' AND Owner.Type = 'User'), we also added WHERE condition on Type field as: AND Owner.Type = 'User'. This is another good way to filter records while dealing with the specific type of related objects we would like to consider. You can even skip the ELSE part if you've already added WHEN-THEN for each related object and the corresponding conditions in WHERE clause.

So that's how you can Simplify SOQL with Polymorphic Relationships. You can have a look at this detailed article from salesforce official documentation to learn more about TYPEOF clause. Before coming to the end of this blog, let's talk about some of the important considerations of TYPEOF clause as well.

Considerations for TYPEOF

I am highlighting some of the considerations of TYPEOF clause here, you can checkout the full list in official documentation.

• TYPEOF cannot be used with with queries that don't return objects such as COUNT() and aggregate queries
• TYPEOF cannot be used in SOQL used in Bulk API
•  TYPEOF cannot be used in semi-join query. Semi Join query is a query used to filter the original query - For example: SELECT Name FROM Contact WHERE AccountId IN (SELECT Id FROM Account), here the text in bold is semi-join query
• TYPEOF cannot be used with a relationship field whose relationshipName or namePointing attribute is false.

You can checkout the namePointing and relationshipName attribute of a field very easily. For example, consider the below code:

System.debug(Case.OwnerId.getDescribe());

Here, we're getting the DescribeFieldResult for OwnerId field of Case object. The output for the same is provided below:

Schema.DescribeFieldResult[
    getByteLength=18;
    getCalculatedFormula=null;
    getCompoundFieldName=null;
    getController=null;
    getDataTranslationEnabled=null;
    getDefaultValue=null;
    getDefaultValueFormula=null;
    getDigits=0;
    getFilteredLookupInfo=null;
    getInlineHelpText=null;
    getLabel=Owner ID;
    getLength=18;
    getLocalName=OwnerId;
    getMask=null;
    getMaskType=null;
    getName=OwnerId;
    getPrecision=0;
    getReferenceTargetField=null;
    getRelationshipName=Owner; // <---- Relationship Name
    getRelationshipOrder=null;
    getScale=0;
    getSoapType=ID;
    getSobjectField=OwnerId;
    getType=REFERENCE;
    isAccessible=true;
    isAggregatable=true;
    isAiPredictionField=false;
    isAutoNumber=false;
    isCalculated=false;
    isCascadeDelete=false;
    isCaseSensitive=false;
    isCreateable=true;
    isCustom=false;
    isDefaultedOnCreate=true;
    isDependentPicklist=false;
    isDeprecatedAndHidden=false;
    isDisplayLocationInDecimal=false;
    isEncrypted=false;
    isExternalId=false;
    isFilterable=true;
    isFormulaTreatNullNumberAsZero=false;
    isGroupable=true;
    isHighScaleNumber=false;
    isHtmlFormatted=false;
    isIdLookup=false;
    isNameField=false;
    isNamePointing=true; // <---- Name Pointing
    isNillable=false;
    isPermissionable=false;
    isQueryByDistance=false;
    isRestrictedDelete=false;
    isSearchPrefilterable=false;
    isSortable=true;
    isUnique=false;
    isUpdateable=true;
    isWriteRequiresMasterRead=false;
]

If you notice, the relationshipName for this field is Owner and namePointing attribute is also true. A smaller documentation on TYPEOF clause is also available here.

That's all for this tutorial. I hope you liked it, let me know your feedback in the comments down below. You can connect with my on Connections app by scanning the QR code given below:

Or search in the code scanner screen using my username: rahulmalhotra

Happy Trailblazing!!

Creating a simple testModal LWC

testModal.js-meta.xml

<?xml version="1.0" encoding="UTF-8"?>
<LightningComponentBundle xmlns="http://soap.sforce.com/2006/04/metadata">
    <apiVersion>55.0</apiVersion>
    <isExposed>true</isExposed>
    <targets>
        <target>lightning__HomePage</target>
    </targets>
</LightningComponentBundle>

testModal.html

<template>
    <lightning-modal-header>Test Modal Header</lightning-modal-header>
    <lightning-modal-body>Test Modal Body</lightning-modal-body>
    <lightning-modal-footer>Test Modal Footer</lightning-modal-footer>
</template>

<lightning-modal-header label="Test Modal Label">Test Modal Header</lightning-modal-header>

Okay that's fine but how do I actually use this as a modal?

testModal.js

import LightningModal from 'lightning/modal';

export default class TestModal extends LightningModal {}

useModal.js-meta.xml

<?xml version="1.0" encoding="UTF-8"?>
<LightningComponentBundle xmlns="http://soap.sforce.com/2006/04/metadata">
    <apiVersion>55.0</apiVersion>
    <isExposed>true</isExposed>
    <targets>
        <target>lightning__HomePage</target>
    </targets>
</LightningComponentBundle>

useModal.html

<template>
    <lightning-card title="Use Modal">
        <p class="slds-var-p-horizontal_small">
            <lightning-button label="Open Modal" onclick={openModal}></lightning-button>
        </p>
    </lightning-card>
</template>

useModal.js

import { LightningElement } from 'lwc';
import TestModal from 'c/testModal';

export default class UseModal extends LightningElement {

    openModal() {
        TestModal.open();
    }
}

Resizing our modal

    TestModal.open({
        size: 'small'
    });

For a medim sized modal, you can just do nothing (as the default size is medium) or pass in the medium value as shown below:

    TestModal.open({
        size: 'medium'
    });

And you'll have the below output:

Similarly, for a large modal, you can just do:

    TestModal.open({
        size: 'large'
    });

And you'll have the below output:

Defining a Custom Close Button for our Lightning Modal

<template>
    <lightning-modal-header>Test Modal Header</lightning-modal-header>
    <lightning-modal-body>Test Modal Body</lightning-modal-body>
    <lightning-modal-footer>
        <lightning-button label="Cancel" onclick={closeModal} class="slds-var-p-right_x-small"></lightning-button>
        <lightning-button label="Save" variant="brand" onclick={save}></lightning-button>
    </lightning-modal-footer>
</template>

import LightningModal from 'lightning/modal';

export default class TestModal extends LightningModal {

    closeModal() {
        this.close();
    }

    save() {
        console.log('We will save the data and then close modal');
    }
}

Prevent the user from closing Lightning Modal using disableClose attribute

import LightningModal from 'lightning/modal';

export default class TestModal extends LightningModal {

    closeModal() {
        this.close();
    }

    save() {
        console.log('We will save the data and then close modal');
        this.disableClose = true;
        const that = this;
        setTimeout(() => {
            console.log('Information saved! You can now close the modal');
            that.disableClose = false;
        }, 5000);
    }
}

<template>
    <lightning-modal-header label="Test Modal Label">Test Modal Header</lightning-modal-header>
    <lightning-modal-body>Test Modal Body</lightning-modal-body>
    <lightning-modal-footer>
        <lightning-button label="Cancel" onclick={closeModal} class="slds-var-p-right_x-small" disabled={disableClose}></lightning-button>
        <lightning-button label="Save" variant="brand" onclick={save} disabled={disableClose}></lightning-button>
    </lightning-modal-footer>
</template>

import LightningModal from 'lightning/modal';

export default class TestModal extends LightningModal {

    closeModal() {
        this.close();
    }

    save() {
        console.log('We will save the data and then close modal');
        this.disableClose = true;
        const that = this;
        setTimeout(() => {
            console.log('Information saved! Closing the modal...');
            that.disableClose = false;
            that.close();
        }, 5000);
    }
}