i am wanting to import an array of json data into my contract on construct. I want to pass it an array of address to be saved into an array in my contract. Is this possible? I have seen a few posts about phrasing json into a contract but could't quite extract what i am looking for.

The json data i have is structured like this; - i am wanting to extract only the HolderAddress's.

    "HolderAddress": "0x00007569643bc1709561ec2e86f385df3759e5dd",
    "Balance": 100,
    "PendingBalanceUpdate": "No"
    "HolderAddress": "0x00089553ab5a08bfdf1dc324845a4ad7a63e26b8",
    "Balance": 9,
    "PendingBalanceUpdate": "No"
    "HolderAddress": "0x0017bf3bca94a016a27d496363cec4d868758bb7",
    "Balance": 650,
    "PendingBalanceUpdate": "No"

Can this data be passed at the deployment of the contract and how would i link the contract to read the json file?

Many thanks

1 Answer 1


ATM, what you can do is:

constructor(address[] memory addresses, uint256[] memory balances, bool[] memory flags) public {
    uint256 length = addresses.length;
    require(length == balances.length, "INVALID_INPUT");
    require(length == flags.length, "INVALID_INPUT");
    for (uint256 i = 0; i < length; i++) {
        // do whatever you want to do with the input data

With arr being the array of objects in your question, you can use:

  • arr.map(x => x.HolderAddress) as the 1st parameter
  • arr.map(x => x.Balance) as the 2nd parameter
  • arr.map(x => x.PendingBalanceUpdate != "No") as the 3rd parameter
  • Thanks for this. How do i initially pass the json to the constructor/contract?
    – Tuck
    Sep 30, 2020 at 15:11
  • @Tuck: See updated answer. Sep 30, 2020 at 15:19
  • Thank you for you time and response. I apologies for for asking obvious and basic questions. This is my first time playing around with json but have been learning solidity for a couple of months. Is this deployed from within the migration.js script? so it would look like deployer.deploy(MyToken, arr.map(x => x.HolderAddress), arr.map(x => x.Balance)); ? Would i also call the json array into the script or have to copy it in?
    – Tuck
    Sep 30, 2020 at 15:35
  • @Tuck: You're missing the last input argument (or maybe you just omitted it in order to keep the question short). As with regards to your last question, I don't understand the meaning of "call the json array into the script". Sep 30, 2020 at 15:46
  • yes just keeping the reply shorter. So i have my array of data in a json file, do i need to import/declare/not sure on the correct term that into the migrations script? Is it best to just copy the whole thing in?
    – Tuck
    Sep 30, 2020 at 15:50

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