Better console/inspect display value of BigNumber

[drortirosh]

currently, doing

console.log(ethers.BigNumber.from(ethers.utils.parseEther('100')))

yields

BigNumber { _hex: '0x056bc75e2d63100000', _isBigNumber: true }

It is better to provide the number in a better form..
I currently have a local helper in my config file:

const inspect_custom_symbol = Symbol.for('nodejs.util.inspect.custom')
// @ts-ignore
BigNumber.prototype[inspect_custom_symbol] = function() { return `BigNumber ${parseInt(this._hex)}` }

which generates a much more readable form:
BigNumber 100000000000000000000

[ricmoo]

That is exactly what the playground.ethers.org does. :)

But not something I would include in the core library, because it is fairly node specific, and depends on the inspect library you are using.

In v6, the display includes the base-10 number though. :)

[fvictorio]

Can't this be done in a way that doesn't cause issues in other environments?

[ricmoo]

They look nicer in v6. :)

But making anything look nicer requires changing the signatures, which almost always causes headaches for downstream dependencies.

[fvictorio]

Hmm, I don't think I understand what you mean. My question is if the nodejs.util.inspect.custom thing couldn't be done in a way that doesn't affect other environments. That shouldn't change any signature, should it?

[ricmoo]

The way that custom.inspect works is by adding a new method to the class, using the symbol defined by inspect.custom as it’s name.

So, adding it to an object changes the object’s prototype, and as a well known symbol it may be in use by other people who wish to format it a specific way (often this is wrapped by an if (!obj[inspect.custom])), so changing the value of this can break code that currently exists out in space.

For example, the playground uses this property with a custom inspector library.

Anyone who wishes to modify their own application though, can easily add a function to BigNumber.prototype[inspect.custom], but making this change to the library itself is not backwards compatible. Bit this is how the playground does it. :)

[mqklin]

I have similar problem. Every value in an object is a BigNumber, and it's impossible to read without parsing it first. (I'm migrating from web3, and there every value was a simple string).

[mqklin]

@ricmoo is there a way to log all BNs in an array/object like a string? Something like console.log(convertBNsToString(myValue))

[ricmoo]

You could also use JSON.stringify in your console.log, as there is a .toJson() method on BigNumber. That might help?

[drortirosh]

Afaik JSON.stringify would return the members _hex and _isBigNumber

[ricmoo]

It looks like you you are right except it’s hex. :s

You can pass in a replacer though, and convert it to whatever format you want.

What is the problem with an object? Just that it’s in hex?

[mqklin]

@ricmoo I wrote a simple (fast and dirty) function that does exactly what I need: https://gist.github.com/mqklin/17b90cd513149c0ad6b2ac673aacbec1
I added it to console global object: console.logBNs = logBNs;
Now my output looks like this:

I like it more that an output from JSON.stringify, because I can use all the benefits from DevTools console (like collapse-uncollapse objects etc)