For Example:

I have a website and on the website there is an input box that allows the user to input a number.

Say he inputs 10, can that number then be passed to an empty variable in the smart contract?

  • read about how to develop a Dapp, in your case you need to use web3js framework. – Badr Bellaj Jul 24 '17 at 14:05

As @Badr Bellaj says, you can use web3.js framework.

Here is a simple example using web3.js and Metamask.

    var contractAddress = "yourContractAddress";
    var abi = JSON.parse('yourContractABI');
    var yourContract;

    window.addEventListener('load', function() {
        // Checking if Web3 has been injected by the browser (Mist/MetaMask)
        if (typeof web3 !== 'undefined') {
            window.web3 = new Web3(web3.currentProvider);
            yourContract = web3.eth.contract(abi).at(contractAddress);

        } else {
            console.log('No web3? You should consider trying MetaMask!')

    //call this function when you want to pass argument to your contract function
    function callYourFunction(){
        var inputData = document.getElementById("IDInputField").value;
        //if your function is a constant function
        yourContract.yourFunction(inputData, function(error, result){


Here is a simple test contract

contract Test{

    function yourFunction(uint256 _value) constant returns (uint256) {
        return _value;

You can read more on:

Contract Methods - https://github.com/ethereum/wiki/wiki/JavaScript-API#contract-methods

sendTransaction - https://github.com/ethereum/wiki/wiki/JavaScript-API#web3ethsendtransaction

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