尝试使用nightmare.js从搜索结果中提取数据，但得到错误："Cannot read property 'click‘of undefined“

Question

我正在尝试解决这个练习：

a)在谷歌搜索中输入"datatables“导航到https://datatables.net/，然后点击正确的结果。

b)您将找到一个包含一些数据的表格示例。请从表中提取/提取数据到数组中。在数组中，您将拥有对象。对象将是表中的一行。对象属性将是来自每个表列的数据。

c)请将数组导出为CSV。

因为我从来没有使用过nightmare.js，所以我用谷歌搜索了一下，找到了我需要的https://github.com/XanderGriff/webscraping-with-nightmare/blob/master/main.mjs，但在一开始它并不起作用，我稍微修改了一下代码，但仍然有错误。

    // Package Definitions
    var csvWriter = require('csv-write-stream');
    var fs = require('fs');
    var Nightmare = require('nightmare');


    // Constant Definitions
    const GOOGLE = 'https://www.google.com';
    const QUERY = 'datatables';
    const SEARCHBAR = 'form[action*="/search"] [name=q]';
    const SEARCHBUTTON = 'form[action*="/search"] [type=submit]';
    const SEARCH_RESULT_ID = 'h3.r > a';
    const DATATABLES_LINK = 'https://datatables.net/';
    const DATATABLES_SIZE_SELECTOR = 'select[name="example_length"]';
    const DATATABLES_DATA_SELECTOR = 'table#example tr';

    (async ()=>{
        let nightmare;
        try {
        nightmare = Nightmare({ show: true });
        await nightmare
            // Navigate to Google
            .goto(GOOGLE)
            .type(SEARCHBAR, QUERY)
            .click(SEARCHBUTTON)
            .wait(SEARCH_RESULT_ID)
            await nightmare.evaluate( (SEARCH_RESULT_ID, 

    DATATABLES_LINK) => {
    // filter results based on css selectors to choose link with 
    proper url
    // indexed at 0 to access element from single-element array 
    produced in above instruction

    (Array.from(document.querySelectorAll(SEARCH_RESULT_ID))).filter(a 
    => a.href === DATATABLES_LINK)[0].click();
                    }, SEARCH_RESULT_ID, DATATABLES_LINK)

            // Adjust datatable to show all entries
                await nightmare
                    .wait(DATATABLES_SIZE_SELECTOR)
                    .select(DATATABLES_SIZE_SELECTOR, 100);

            // Retrieve values from datatable
            await nightmare.evaluate( (DATATABLES_DATA_SELECTOR) => {
                let table_rows = 
    Array.from(document.querySelectorAll(DATATABLES_DATA_SELECTOR));
    // delineate between keys and vals from retrieved table data
                let table_keys_row = 
    Array.from((table_rows[0]).querySelectorAll('th')).map(e => 
    e.innerHTML); //array of strings
                let table_data_rows = table_rows.slice(1,58); //array 
    of arrays of HTML elements

                let array_of_row_objects = [];
                let row_object = {};
                let formatted_values = [];

                table_data_rows.forEach( row => {
                // grab innerHTML from each element in the row
                    formatted_values = 
    Array.from(row.querySelectorAll('td')).map(e => e.innerHTML);

    // place each of the element values in an object with each value 
    associated with its respective key 
                    row_object = {};
                    for(i = 0; i < table_keys_row.length; i++) {
                        row_object[table_keys_row[i]] = 
    formatted_values[i];
                    }

                    array_of_row_objects.push(row_object);
                })

                    return array_of_row_objects;
                }, DATATABLES_DATA_SELECTOR)

                // Write to CSV
                writer.pipe(fs.createWriteStream('output.csv'));
                result.forEach( obj => {
                    writer.write(obj);
                });
                writer.end();

                console.log("Wrote values to CSV...")
            } catch (error) {
                console.error(error);
                throw error;
            } finally {
                await nightmare.end();
            }
    })();

我使用DEBUG=nightmare运行代码，并收到以下代码：

    nightmare queuing process start +0ms
    nightmare queueing action "goto" for https://www.google.com +3ms
    nightmare queueing action "type" +0ms
    nightmare queueing action "click" +0ms
    nightmare queueing action "wait" +0ms
    nightmare running +1ms
    nightmare queueing action "evaluate" +5s
    nightmare running +1ms
    { TypeError: Cannot read property 'click' of undefined
    at fn (<anonymous>:8:106)
    at javascript (<anonymous>:23:21)
    at <anonymous>:38:3
    at EventEmitter.electron.ipcRenderer.on 
(/home/anna/automation/node_modules/electron/dist/resources/electron.a 
    sar/renderer/web-frame-init.js:36:30)
    at emitMany (events.js:147:13)
    at EventEmitter.emit (events.js:224:7) code: -1 }
    nightmare running +12ms
    nightmare electron child process exited with code 0: success! 
    +55ms
    (node:10610) UnhandledPromiseRejectionWarning: TypeError: Cannot 
    read property 'click' of undefined
    at fn (<anonymous>:8:106)
    at javascript (<anonymous>:23:21)
    at <anonymous>:38:3
    at EventEmitter.electron.ipcRenderer.on 
 (/home/anna/automation/node_modules/electron/dist/resources/electron. 
    asar/renderer/web-frame-init.js:36:30)
    at emitMany (events.js:147:13)
    at EventEmitter.emit (events.js:224:7)
    (node:10610) UnhandledPromiseRejectionWarning: Unhandled promise 
    rejection. This error originated either by throwing inside of an 
    async function without a catch block, or by rejecting a promise 
    which was not handled with .catch(). (rejection id: 1)
    (node:10610) [DEP0018] DeprecationWarning: Unhandled promise 
    rejections are deprecated. In the future, promise rejections that 
    are not handled will terminate the Node.js process with a non-zero 
    exit code.

如果有人知道或面临这个问题，请帮我弄清楚。

Answer 1

var csvWriter = require('csv-write-stream');
var writer = csvWriter();
var fs = require('fs');
var Nightmare = require('nightmare');

(async () => {
    let nightmare;
    try {
    nightmare = Nightmare({ show: true });
    await nightmare
        .goto('https://www.google.com')
        .type('form[action*="/search"] [name=q]', 'datatables')
        .click('form[action*="/search"] [type=submit]')
        .wait(2500)
        await nightmare.evaluate( () => {
            var link = document.querySelector(".r a");
            link.click();
        })
        await nightmare
            .wait('select[name="example_length"]')
            .select('select[name="example_length"]', 100);

        await nightmare.evaluate( () => {
            let tableRows = Array.from(document.querySelectorAll('table#example tr'));
            let tableKeysRow = Array.from((tableRows[0]).querySelectorAll('th')).map(e => e.innerHTML); 
            let tableDataRows = tableRows.slice(1,58); 
            let arrayOfRowObjects = [];
            let rowObject = {};
            let formattedValues = [];

            tableDataRows.forEach( row => {
                formattedValues = Array.from(row.querySelectorAll('td')).map(e => e.innerHTML);
                rowObject = {};
                for(i = 0; i < tableKeysRow.length; i++) {
                    rowObject[tableKeysRow[i]] = formattedValues[i];
                }

                arrayOfRowObjects.push(rowObject);
            })

                return arrayOfRowObjects;
            })
            .then( result => {
                writer.pipe(fs.createWriteStream('outputData.csv'));
                result.forEach( obj => {
                    writer.write(obj);
                });
                writer.end();
            })
        } catch (error) {
            console.error(error);
            throw error;
        } finally {
            await nightmare.end();
        }
})();