var contract_address =\n“0x0EfBae3f8e3bc34b4A77E07c75dFd9f9A32f6bA2”;<\/p>\n\n\n\n
Next, we will initialize a variable with the contract details in JSON format. To get these details, click the Show Interface<\/em> icon, as shown below, on the contract page and you will the relevant contract information in JSON format. <\/p>\n\n\n\n We have defined the contract_abi variable and initialized it with the\nabove contract details.<\/p>\n\n\n\n var contract_abi = [ { “constant”: true,\n“inputs”: [], “name”: “fundingproject”,\n“outputs”: [ { “name”: “name”, “type”:\n“string”, “value”: “g” }, { “name”:\n“email”, \u2026.. “payable”: false, “type”:\n“constructor” } ]<\/p>\n\n\n\n Next, we create the Web3 instance by providing the endpoint\naddress of our running Ethereum\ninstance.<\/p>\n\n\n\n web3 = new Web3(new\nWeb3.providers.HttpProvider(“http:\/\/127.0.0.1:8545”));<\/p>\n\n\n\n Next, we create the instance of contract by providing the contract\ndetails as part of contract_abi variable \nand address of the contract.<\/p>\n\n\n\n var contract_instance =\nweb3.eth.contract(contract_abi).at(contract_address);<\/p>\n\n\n\n In our HTML page, we have added a button named Stop Fund Raising<\/em>, once clicked will invoke the getStatus()<\/em> method. The getStatus()<\/em> method calls the stopFundRaising()<\/em> method on the contract\ninstance. To execute the operations on the contract, we also provide the\naccount (the Main Account for this example), which would pay the transaction\nfee to execute this transaction on the blockchain network. While running this,\nreplace the \u2018passw0rd\u2019<\/em> value in the unlockAccount<\/em> method below, with the\npassword of your Main account.<\/p>\n\n\n\n The following shows the getStatus()<\/em> method.<\/p>\n\n\n\n Now, once the stopFundRaising<\/em> method is executed, the transaction will be committed as a block in the blockchain network. As we are running this on the local network, it shouldn\u2019t take more than a minute or so to execute. To track the transaction, we will store the returned hashed value of the submitted transaction. We then call the getTransactionReceipt() <\/em>method passing the hash value as a parameter. The said method will be invoked recursively every one minute to check for the valid returned object. If the method returns a valid object, it implies the block is committed, and the transaction is complete. The following code snippet shows the checkHashStatus()<\/em> which makes a call to the getTransactionReceipt() <\/em>of the web3 API:<\/p>\n\n\n\n We also print the response from the getTransactionReceipt()<\/em> method on the\nbrowser console, and you can verify the hash, block number, address (contract\naddress) and other details like gas used for this transaction.<\/p>\n\n\n\n {blockHash:\n“0x739f8a73aa5e7ccca62be65d2f43be732c82ac02693d298ce2af64354be9ee1b”,\nblockNumber: 39659, contractAddress: null, cumulativeGasUsed: 32083, from:\n“0x6b8dc00c09dd3c240c0b964ccec6baf07ab038a5”, to:”0x290298bf15d9546850161e3046233801f2488523″\u2026}<\/p>\n\n\n\n Once we receive the transaction receipt, we print the status of the\nproject on the html page as shown below. The status is fetched by invoking the getProjectStatus()<\/em> method on the\ncontract instance. The method returns the status as \u2018Funding Stopped\u2019.<\/p>\n\n\n\n document.getElementById(“status”).innerText = contract_instance.getProjectStatus();<\/p>\n\n\n\n This completes one end-to-end transaction\nof a web application invoking a smart contract. <\/p>\n\n\n\n Note – The above example uses ether\ntokens for crowdfunding. As a next step, you can create your own digital token\nfor crowdfunding. You can extend the ECR20 Token Contract (https:\/\/theethereum.wiki\/w\/index.php\/ERC20_Token_Standard<\/a>) as the starting point to create\nyour own Initial Coin offering (ICO) and club it with the crowd funding\ncontract logic, which will use your\ncoins for fund raising. Investors\/Participant would invest in your idea by\nbuying your tokens with a hope that their investment and value in tokens\nmultiplies based on the success of the funded project.<\/p>\n\n\n\n![\"\"](\"https:\/\/navveenbalani.dev\/wp-content\/uploads\/2019\/12\/image-61.png\")
<\/figcaption><\/figure>\n\n\n\nfunction getStatus() {\n\n\/\/Unlock main Ether Base account and replace password with your account password\n\/\/This is a demo setup only, get this value through secured login credentials in actual environment\n web3.personal.unlockAccount(web3.eth.accounts[0], 'passw0rd');\n\/\/Call the Stop Fund Raising method\n contract_instance.stopFundRaising({from: web3.eth.accounts[0]}, function(error, result) {\n if(error) {\n console.error(error);\n } else {\n var hash = result;\n console.log(\"hash\"+hash);\n checkHashStatus(hash, updateStatusFromContract);\n }\n });\n }\n<\/code><\/pre>\n\n\n\nfunction checkHashStatus(hash, callback) {\nweb3.eth.getTransactionReceipt(hash, function(error, rcpt) {\n if(error) {\n console.error(error);\n } else {\n if(rcpt == null) {\n setTimeout(function() {\n\/\/call iteratively till hash matches and block is mined\n checkHashStatus(hash, callback);\n }, 1000);\n } else {\n console.log(rcpt)\n \/\/call the function once block is committed\n callback();\n }\n }\n })\n }\n<\/code><\/pre>\n\n\n\n
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