我想在 get 方法中使用 promise 返回值。 nodejs休息api

Question

I am creating a rest api. My get method will return the result according to the total supply value of the contract or it will not respond, but the request I made to the contract returns a promise. How can I use this value?

const NameContract = new web3.eth.Contract(abi, '0xE3A2beCa..........1D901F8');
NameContract.methods.totalSupply().call().then(value => console.log(value))


app.get('/:id', (req, res) => {
    let id = parseInt(req.params.id);
    //I want to use an if here. 
    //I want to throw the query according to the value returned from above,
    // but it returns a promise, how can I use it value?
    nft.findOne({ id: id }, (err, doc) => {
        if (doc != null) {
            res.json(doc)
        }
        else {
            res.status(404).json(err)
        }
    });

});

Answer 1

Try saving the promise whose value will end up being the total value

 const pTotalSupply = NameContract.methods.totalSupply().call();

(assuming this is valid - the .call method looks a little strange). Options then are to

• Not start the server until pTotalSupply above has been fulfilled, provided total supply is a static value and there to be only one name contract the server has to deal with,
• Wait for the result to be obtained within the app.get handler, either by using an await operator inside an asynchronous function body, or wrapping request processing in a promise then argument function, or
• Using a promise then call to save the supply value and call next in a two part app.get handler. This is more an express oriented solution using a pattern along the lines of:

app.get('/:id', (req, res, next) => {
    pTotalSupply.then( value => {
        res.locals.value = value;
        next();
    }
    .catch( err => res.status(500).send("server error")); // or whatever
 }
 , (req, res) => {
    const value = res.locals.value;
    let id = parseInt(req.params.id);
    // process request with value and id:
    ...
 });

The second option is covered in answers to How to return the response from an asynchronous call