[SalesForce] LWC Date Picker – Year Display in

You have misunderstood the HTMLElement.focus() method. The HTMLElement.focus() method sets focus on the specified element, if it can be focused. In other word, It sets the element as the active element in the current document.

See the code below:-

<template>
    <lightning-input type="date" class="date-input" label="date" onfocus={handlefocus}></lightning-input>
    <lightning-button label="set focus" title="Non-primary action" onclick={handleClick} class="slds-m-left_x-small"></lightning-button>        
</template>

What i have checked here is added onfocus event directly to input field. Whenever you click the button, it fires the onfocus event.

The issue is here this.CurrentDate.getMonth().

The month starts with 0 and not 1.

0 -> Jan
1 -> Feb
.
.
10 -> Nov
11 -> Dec

Src: https://www.w3schools.com/jsref/jsref_getmonth.asp

Thus to fix your code, you have to add 1 in your month when you create full date.

this.fulldate = this.CurrentDate.getFullYear() +'-'+(this.CurrentDate.getMonth()+1)+'-'+this.CurrentDate.getDate();

Playground Link: https://developer.salesforce.com/docs/component-library/tools/playground/o3_Lrf0N/4/edit