When I try to pass address as parameter to this addEmployee function it gives me this error:

invalid opcode
    The execution might have thrown.
    Debug to get more information.
modifier onlyOwner()
    require(msg.sender==owner,"msg.sender is not the Owner");

function addEmployee(address payable employeeWallet) onlyOwner external
    emp[emp.length-1] = employeeWallet;
  • An Invalid Opcode exception is the result of either one of two things: 1. An assert(cond) statement, where cond evaluates to false. 2. An array[n] statement, where n exceeds the boundaries of the array (i.e., n < 0 || n >= array.length). So when you get this type of exception, always look for either one of those two "things" in your code. Sep 30, 2019 at 8:56

1 Answer 1


(This is just an educated guess, to be 100% certain I'd need to see your entire contract and the series of calls leading up to the error)

An INVALID opcode is raised when you attempt to access a storage location that hasn't been intialized. In this case, you are attempting to store data in a dynamic array emp at location emp.length-1. Because the length of emp is zero, the calculation emp.length-1 underflows and the EVM reverts when it cannot access emp[2^256-1].

As an alternative, I suggest using emp.push(employeeWallet) for appending the new value to the array.

Useful reading:

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