Solving the Web3.js BigNumber Issue for Large Exponents in JavaScript

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The Problem at Hand

While working with numbers that require high precision, such as cryptocurrency balances, the common issue is as follows:

You retrieve a number (like balance) from an API, which is often in exponential form, such as 9.886999999999999e+ 29.

Trying to convert this number directly into a BN instance using BN.js fails and triggers an error message pertaining to assertion failures.

In this case, you need a solution to convert your exponential number into a proper format that BN.js can accept, ensuring you can further manipulate it as required for your application.

Step-by-Step Solution

Why the Error Occurs

BN.js does not accept numbers in an exponential format. This limitation can lead to the assertion error you've encountered. To work around this issue, we can convert the number to a string format that BN.js can handle correctly.

Solution Steps

Here’s how to resolve the issue effectively:

Convert the Exponential Number to String

Use JavaScript's built-in .toLocaleString() method to convert the exponential numeral into a full number string format that avoids the pitfalls of floating-point representation.

[[See Video to Reveal this Text or Code Snippet]]

Create a BN Instance

After conversion, create a BN instance using the string representation rather than the number itself:

[[See Video to Reveal this Text or Code Snippet]]

Using the Correct Format with fromWei

Finally, once you convert the balance appropriately, you can proceed to manipulate it as needed, such as converting it from Wei to Ether:

[[See Video to Reveal this Text or Code Snippet]]

Recommended Approach

A cleaner approach to avoid the conversion altogether is to ensure that your server endpoint /balanceOf-TKN-by-addr returns the balance as a string. This avoids any need for conversion on the client-side and allows for a straightforward instantiation of your BN object.

[[See Video to Reveal this Text or Code Snippet]]

Conclusion