interact with a smart contract without having a wallet

Question

I have a smart contract that basically store a document and I integrated it with a user interface that let the user go to the website and search for that document .. very simple idea.

I want to let the user use my website without having a wallet since no gas require (only read)

I tried creating an instance of the contract:

        var contract
        var addresse = //my contract addresse;
        var api = // api ;

        contract = new web3.eth.contract(api, addresse); 

but when a i tried to use the website it say:

(index):240 Uncaught TypeError: Cannot read property 'isEntity' of undefined

here my code:

var contract;

    var addresse = "0xDf6E7A02DC7457B7C1c534159305662B63794958";
    var api = [
{
    "constant": false,
    "inputs": [
        {
            "internalType": "string",
            "name": "stdID",
            "type": "string"
        }
    ],
    "name": "deleteCertificate",
    "outputs": [
        {
            "internalType": "bool",
            "name": "success",
            "type": "bool"
        }
    ],
    "payable": false,
    "stateMutability": "nonpayable",
    "type": "function"
},
{
    "constant": false,
    "inputs": [
        {
            "internalType": "string",
            "name": "certID",
            "type": "string"
        },
        {
            "internalType": "string",
            "name": "stdID",
            "type": "string"
        },
        {
            "internalType": "string",
            "name": "stdName",
            "type": "string"
        },
        {
            "internalType": "uint256",
            "name": "nID",
            "type": "uint256"
        },
        {
            "internalType": "string",
            "name": "collage",
            "type": "string"
        },
        {
            "internalType": "string",
            "name": "stdGPA",
            "type": "string"
        },
        {
            "internalType": "string",
            "name": "gradYear",
            "type": "string"
        }
    ],
    "name": "newCertificate",
    "outputs": [
        {
            "internalType": "bool",
            "name": "success",
            "type": "bool"
        }
    ],
    "payable": false,
    "stateMutability": "nonpayable",
    "type": "function"
},
{
    "inputs": [],
    "payable": false,
    "stateMutability": "nonpayable",
    "type": "constructor"
},
{
    "constant": true,
    "inputs": [
        {
            "internalType": "string",
            "name": "stdID",
            "type": "string"
        }
    ],
    "name": "getCartID",
    "outputs": [
        {
            "internalType": "string",
            "name": "",
            "type": "string"
        }
    ],
    "payable": false,
    "stateMutability": "view",
    "type": "function"
},
{
    "constant": true,
    "inputs": [
        {
            "internalType": "string",
            "name": "certID",
            "type": "string"
        },
        {
            "internalType": "string",
            "name": "stdID",
            "type": "string"
        }
    ],
    "name": "getCertificateInfo",
    "outputs": [
        {
            "internalType": "string",
            "name": "",
            "type": "string"
        },
        {
            "internalType": "string",
            "name": "",
            "type": "string"
        },
        {
            "internalType": "uint256",
            "name": "",
            "type": "uint256"
        },
        {
            "internalType": "string",
            "name": "",
            "type": "string"
        },
        {
            "internalType": "string",
            "name": "",
            "type": "string"
        },
        {
            "internalType": "string",
            "name": "",
            "type": "string"
        }
    ],
    "payable": false,
    "stateMutability": "view",
    "type": "function"
},
{
    "constant": true,
    "inputs": [
        {
            "internalType": "string",
            "name": "stdID",
            "type": "string"
        }
    ],
    "name": "isEntity",
    "outputs": [
        {
            "internalType": "bool",
            "name": "isIndeed",
            "type": "bool"
        }
    ],
    "payable": false,
    "stateMutability": "view",
    "type": "function"
}

]; contract = new web3.eth.contract(api, addresse);

    function getDou(){

        var certHolder = document.getElementById("certInput").value;
        var isExist = contract.methods.isEntity(certHolder).call().then(function (result) {
            if(result){
                contract.methods.getCartID(certHolder).call().then(function(result){   
                    document.getElementById("getDoc").innerHTML = result;
                });
            }else{
                alert("The document does not exist!!");
                location.reload();
            }
        }).catch(function (err) {
        console.log(err.message);
        });    
    }

note: the code work fine when I added this before the contract

web3 = new Web3(web3.currentProvider);

but i think this will not work for the users

Answer 1

Ethers.js uses a different approach that I believe provides developers more flexibility.

Try with this code after npm i ethers and renaming your variable api-> abi

//Load ethers
const ethers = require('ethers');


async function isEntity(entity) {
// Connect to the network
const provider = ethers.getDefaultProvider("homestead");

// The address of the smart contract
const contractAddress = "0xDf6E7A02DC7457B7C1c534159305662B63794958";

// We connect to the Contract using a Provider, so we will only
// have read-only access to the Contract
const contract = new ethers.Contract(contractAddress, abi, provider);


return await contract.isEntity(entity);

}