Question

考虑例子：

JS

"use strict";

const input = [
    "https://www.google.ru",
    "https://www.google.ru",
    "https://www.google.ru",
    "https://www.google.ru",
    "https://www.google.ru"
];
const createPhantomPool = require('phantom-pool');
(async function() {
    console.log("start");
    const pool = createPhantomPool({max: input.length*2, min: input.length*2});
    let promises = [];
    input.forEach(url => promises.push(pool.use(async (instance) => {
        instance.createPage()
            .then(page => {
                return page.open(url);
            }).then(() => console.log("load finished"))
            .catch(error => {
                console.log(error);
            });
    })));
    await (Promise.all(promises).then(() => console.log("after then")));
    console.log("end");
}());

的package.json

"dependencies": {
  "aws-sdk": "^2.68.0",
  "es6-promise": "^4.1.0",
  "log4js": "^1.1.1",
  "moment-timezone": "^0.5.13",
  "phantomjs": "^2.1.7",
  "webpage": "^0.3.0"

我预计所有承诺都将完成，并且仅在调用console.log("after then")之后。但是这个例子给了我以下输出：

start
after then
end
load finished
load finished
load finished
load finished
load finished

为什么在after then ???

之前打印load finished

Answer 1

您需要await来自pool.use

的instance.createPage()承诺

"use strict";

const input = [
    "https://www.google.ru",
    "https://www.google.ru",
    "https://www.google.ru",
    "https://www.google.ru",
    "https://www.google.ru"
];
const createPhantomPool = require('phantom-pool');
(async function() {
    console.log("start");
    const pool = createPhantomPool({max: input.length*2, min: input.length*2});
    let promises = [];
    input.forEach(url => promises.push(pool.use(async (instance) => {
        await instance.createPage()
            .then(page => {
                return page.open(url);
            }).then(() => console.log("load finished"))
            .catch(error => {
                console.log(error);
            });
    })));
    await (Promise.all(promises).then(() => console.log("after then")));
    console.log("end");
}());

pool.use

这已经过测试。发生了什么instance.createPage()不等待return解决的承诺。您要么await承诺，要么async承诺。您已经将它的包装器作为await函数使用，因此可以保持一致并且du -hsc * | sort -h它。

如何在javascript中等待Promise.all.then后调用代码？

1 个答案: