Question

我有一个temp数组的以太坊地址。我想用一个返回promise（web3方法）的函数映射这个数组。在Promise.all之后，承诺仍然悬而未决。我不明白为什么。

以下是我的相关代码：

var prom = temp.map(x => [x, self.getBalance(x)]);

Promise.all(prom).then(function(results) {
    console.log(results)
});

getBalance(t){
    return this.contract.methods.balanceOf(t).call().then(function (result) {
        return result / Math.pow(10, 18);
    }).catch(function(e) {
        console.log('error: '+e);
    });
}

结果：

[ [ '0x92c9F71fBc532BefBA6dA4278dF37CC3A81c1fAD',
    Promise { <pending> } ],
  [ '0x910a2b76F4979FeBB4b589fA8D55e6866f4e565D',
    Promise { <pending> } ] ]

Answer 1

如果您想在退回的结果中加入x，只需在第一个承诺中添加then()并将其包含在内：

let temp =['0x92c9F71fBc532BefBA6dA4278dF37CC3A81c1fAD','0x910a2b76F4979FeBB4b589fA8D55e6866f4e565D'];

// return x with the promise result
var prom = temp.map(x => getBalance(x).then(r => [x,r]));

Promise.all(prom).then(function(results) {
    console.log(results)
});

function getBalance(x){
    // fake get balance
    return Promise.resolve(Math.random() + 10)
}

Answer 2

你在地图中返回一个数组数组，而不是一系列的promises，它应该是：

var prom = temp.map(x => self.getBalance(x));
Promise.all(prom).then(function(balances) {
   console.log(balances.map((balance, i) => [temp[i], balance]));
});

或使用async/await

 const prom = temp.map(async x => [x, await getBalance(x)]);

 Promise.all(prom)
    .then(balances => console.log(balances));

＆＃13;

const temp = [
  '0x92c9F71fBc532BefBA6dA4278dF37CC3A81c1fAD',
  '0x910a2b76F4979FeBB4b589fA8D55e6866f4e565D'
];

const getBalance = address => {
  return Promise.resolve(Math.random());
};

const prom = temp.map(async x => [x, await getBalance(x)]);

Promise.all(prom)
    .then(balances => console.log(balances));

＆＃13;

在地图功能中使用promises

2 个答案: