How to get Salesforce Base URL in Lightning Web Component

To get Salesforce base URL use the window.location object can be used to get the current page address (URL).
The window.location.origin property returns the origin URL of the current page.

baseURL.html:

<template>
    <lightning-card title="Salesforce Base URL in Lighting Web Component">
        <div class="slds-text-heading_medium slds-text-align-center">
            SFDC Base URL : <p></p><lightning-formatted-url value={sfdcBaseURL} ></lightning-formatted-url></p>
        </div>
    </lightning-card>

</template>

baseURL.js:

import { LightningElement } from 'lwc';
export default class BaseURL extends LightningElement {
    sfdcBaseURL;
    renderedCallback() {
        this.sfdcBaseURL = window.location.origin;
    }

}
baseURL.js-meta.xml:

<?xml version="1.0" encoding="UTF-8"?>
<LightningComponentBundle xmlns="http://soap.sforce.com/2006/04/metadata">
    <apiVersion>48.0</apiVersion>
    <isExposed>true</isExposed>
    <targets>
        <target>lightning__AppPage</target>
        <target>lightning__RecordPage</target>
        <target>lightning__HomePage</target>
    </targets>

</LightningComponentBundle>

Output:

Getting Current Logged in User information in Lightning Web Component(lwc)

userDetails.html:

<template>
    <lightning-card title="Current Logged User Information">
        <template if:true={objUser}>
            <dl class="slds-list_horizontal slds-wrap" style="margin-left: 3%;">
                <dt class="slds-item_label slds-truncate" title="First Name">First Name:</dt>
                <dd class="slds-item_detail slds-truncate"><b>{objUser.FirstName}</b></dd>
                <dt class="slds-item_label slds-truncate" title="Last Name">Last Name:</dt>
                <dd class="slds-item_detail slds-truncate"><b>{objUser.LastName}</b></dd>
                <dt class="slds-item_label slds-truncate" title="Full Name">Name:</dt>
                <dd class="slds-item_detail slds-truncate"><b>{objUser.Name}</b></dd>
                <dt class="slds-item_label slds-truncate" title="Alias">Alias:</dt>
                <dd class="slds-item_detail slds-truncate"><b>{objUser.Alias}</b></dd>
                <dt class="slds-item_label slds-truncate" title="Active">Is Active:</dt>
                <dd class="slds-item_detail slds-truncate"><b>{objUser.IsActive}</b></dd>
            </dl>
        </template>
    </lightning-card>

</template>

userDetails.js:

import { LightningElement, track, wire} from 'lwc';

// To get the record details based on record id
import { getRecord } from 'lightning/uiRecordApi';

// impoting USER id
import USER_ID from '@salesforce/user/Id'; 

export default class CurrentUserDetailsInLWC extends LightningElement {

    @track objUser = {};
    
    // using wire service getting current user data
    @wire(getRecord, { recordId: USER_ID, fields: ['User.FirstName', 'User.LastName', 'User.Name', 'User.Alias', 'User.IsActive'] })
    userData({error, data}) {
        if(data) {
            window.console.log('data ====> '+JSON.stringify(data));

            let objCurrentData = data.fields;

            this.objUser = {
                FirstName : objCurrentData.FirstName.value,
                LastName : objCurrentData.LastName.value,
                Name : objCurrentData.Name.value,
                Alias : objCurrentData.Alias.value,
                IsActive : objCurrentData.IsActive.value,
            }
        } 
        else if(error) {
            window.console.log('error Occured====> '+JSON.stringify(error))
        } 
    }


}
userDetails.js-meta.xml:

<?xml version="1.0" encoding="UTF-8"?>
<LightningComponentBundle xmlns="http://soap.sforce.com/2006/04/metadata">
    <apiVersion>48.0</apiVersion>
    <isExposed>true</isExposed>
    <targets>
        <target>lightning__AppPage</target>
        <target>lightning__RecordPage</target>
        <target>lightning__HomePage</target>
    </targets>

</LightningComponentBundle>