How to set values for Solidity contract state variables from JavaScript front-end?

I am trying to set values to the following contract public state variables from a frontend javascript code. But it seems not working.

Contract public state variables:

// Current state of the auction.
address public highestBidder;
uint public highestBid;

In the below Javascript code, I get the values for address and amount from UI and assign to highestBidder & highestBid. But it seems not working. How do I do this?

// Submit bid details, triggered by the "Bid" button
SimpleAuction.prototype.startAuction = function() {
    console.log("inside startAuction");
    var that = this;
    console.log("inside startAuction");
    // Gets form input values
    var address = $("#enter-address").val();
    var amount = $("#enter-amount").val();
    console.log(amount);

    // Validates address using utility function
    if (!isValidAddress(address)) {
        console.log("Invalid address");
        return;
    }
    that.highestBidder = address;
    
     
    // Validate amount using utility function
    if (!isValidAmount(amount)) {
        console.log("Invalid amount");
        return;
    }
    that.highestBid = amount;

This code fixed the issue. Passing address and amount as a transaction object in the bid() function in JS

// Submit bid details, triggered by the "Bid" button
SimpleAuction.prototype.startAuction = function() {
    console.log("inside startAuction");
    var that = this;
    console.log("inside startAuction");
    // Gets form input values
    var address = $("#enter-address").val();
    var amount = $("#enter-amount").val();
    console.log(amount);

    // Validates address using utility function
    if (!isValidAddress(address)) {
        console.log("Invalid address");
        return;
    }
     
    // Validate amount using utility function
    if (!isValidAmount(amount)) {
        console.log("Invalid amount");
        return;
    }
    
    
    // Calls the public `bid` function from the smart contract
    this.instance.bid(
         {  
            from: address,
            value: amount,
            gas: 100000,
            gasPrice: 100000,
            gasLimit: 100000
        },
       
        function(error, txHash) {
            if (error) {
                console.log(error);
            }
            // If success, wait for confirmation of transaction,
            // then clear form values
            else {
                that.waitForReceipt(txHash, function(receipt) {
                    if (receipt.status) {
                        $("#enter-address").val("");
                        $("#enter-amount").val("");
                    } else {
                        console.log("error");
                    }
                });
            }
        }
    );
};

function setHighestBidder(address _highestBidder) {
    highestBidder = _highestBidder;
}