When JS passes numeric values as arguments to Solidity function, why is it better to wrap them in quotes?

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I defined a function in Solidity:

function store(uint256 _favoriteNumber) public {}

Then call the function with argument 7 in JavaScript:

contract.store(7);

But, according to the Patrick Collins JS video, it's better to wrap number 7 with quotes like this:

contract.sotre("7");

So here are two things confused me:

  1. Why it's better to wrap number with quotes when passing a number to a solidity contract function?
  2. Why ehter.js can automatically convert string to number?
ethers.js smartcontracts solidity javascript
1 Answers

Javascript supports a smaller set of numbers than Solidity. Specificially, the maximal safe value in JS is 2^53 - 1, while the maximal numeric value in Solidity is 2^256.

So if you were to for example transfer 1 token with 18 decimals, the resulting decimal value that you'd need to pass to the Solidity contract is 1000000000000000000 - which is somewhere between 2^59 and 2^60, already higher than the maximal safe JS integer of 2^53 - 1.

For this reason, ethers.js and other JS smart contract libraries accept numeric values either as native JS string or an instance of a helper library called BigNumber - but not as integers.

Note: Some libraries in some versions might be able to convert the native integer to a string or BigNumber at first. But generally, it's always safer to pass the non-integer values.

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