Exploring Typescript code through a practical example with reference to Uniswap's implementation

On the Uniswap website, I came across some code on the Swap page that caught my attention. You can find the code snippet in question at line 115 of the Uniswap GitHub repository.

const {
    trade: { state: tradeState, trade },
    allowedSlippage,
    currencyBalances,
    parsedAmount,
    currencies,
    inputError: swapInputError,
} = useDerivedSwapInfo()

As someone with limited knowledge of TypeScript, it appears to me that this code is destructuring the output of the useDerivedSwapInfo() function call. One particular variable, trade, is defined as having a type of { state: tradeState, trade }. However, the way tradeState and the separate 'trade' variable are used later in the code seems confusing.

Can someone provide insight into what exactly the line 

trade: { state: tradeState, trade }
is intended to achieve?

typescript

Answer №1

  1. The result of calling useDerivedSwapInfo() is being broken down into individual variables.

Ah, you got it right!

  1. One of the variables is trade which consists of { state: tradeState, trade }.

Actually, I understand where the confusion arose. It seems like nested destructuring with variable renaming is happening here. Essentially, it's extracting x.trade.state and x.trade.trade from trade in the return value of useDerivedSwapInfo() function.

If we were to rewrite this without destructuring, it would look something like:

const x = useDerivedSwapInfo();
const tradeState = x.trade.state;
const trade = x.trade.trade;
const allowedSlippage = x.allowedSlippage;
const currencyBalance = x.currencyBalances;
const parsedAmount = x.parsedAmount;
const currencies = x.currencies;
const swapInputError = x.inputError;

(Note that x.trade wouldn't be accessed twice in reality.)

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