Custom validation in Lightning web component

getinputval.js

/* Method to get input field value */
getinputval() {
    let returnvalue; //assigning temp variable
    var inputCmp = this.template.querySelector(".inputfield"); //getting element
    var value = inputCmp.value; //assigning value to variable
    // is input valid text?
    if (value === "") {
        //adding custom validation
        inputCmp.setCustomValidity("Field is Required!");
        returnvalue = false;
    } else {
        //Removing validation error
        inputCmp.setCustomValidity(""); // if there was a custom error before, reset it
        returnvalue = this.datevalue;
    }
    inputCmp.reportValidity(); // Tells lightning-input to show the error right away without needing interaction

    return returnvalue; // returning inputvalue
}