How to chain a variable amount of methods on node js?

Question

I'm using Nightmarejs to scrap a website. I want to chain multiple operations (promises?) depending on some input. Take the following code:

var Nightmare = require('nightmare');       
var nightmare = Nightmare({ show: true });

nightmare
   .goto('https://www.servipag.com/')
   .select('select#servicios.txt_formulario', '29')
   .wait(200)
   .select('select#billers', '700')
   .insert('input#identificador','60957924')
   .click('#formPagoCuentas a[href^="javascript:AgregarCuentasaPagar"]')
   .wait(10)
   .click('#formPagoCuentas a[href^="javascript:enviar"]')
   .wait('fieldset')
   .evaluate(function () {
     return document.querySelector('.txt_detalle_boleta').innerHTML;
   })
   .end()
   .then(function (result) {
     console.log(result);
   })
   .catch(function (error) {
     console.error('Search failed:', error);
   });

I want to be able to attach a variable amount of times (from 1 to 15) the following lines:

   .select('select#servicios.txt_formulario', '29')
   .wait(200)
   .select('select#billers', '700')
   .insert('input#identificador','60957924')
   .click('#formPagoCuentas a[href^="javascript:AgregarCuentasaPagar"]')
   .wait(10)

so the overall code for four times would be:

var Nightmare = require('nightmare');       
var nightmare = Nightmare({ show: true });

nightmare
   .goto('https://www.servipag.com/')
   // -- repeat this 4 times
   .select('select#servicios.txt_formulario', '29')
   .wait(200)
   .select('select#billers', '700')
   .insert('input#identificador','60957924')
   .click('#formPagoCuentas a[href^="javascript:AgregarCuentasaPagar"]')
   .wait(10)
   // ---
   .select('select#servicios.txt_formulario', '29')
   .wait(200)
   .select('select#billers', '700')
   .insert('input#identificador','60957924')
   .click('#formPagoCuentas a[href^="javascript:AgregarCuentasaPagar"]')
   .wait(10)
   // ---
   .select('select#servicios.txt_formulario', '29')
   .wait(200)
   .select('select#billers', '700')
   .insert('input#identificador','60957924')
   .click('#formPagoCuentas a[href^="javascript:AgregarCuentasaPagar"]')
   .wait(10)
   // ---
   .select('select#servicios.txt_formulario', '29')
   .wait(200)
   .select('select#billers', '700')
   .insert('input#identificador','60957924')
   .click('#formPagoCuentas a[href^="javascript:AgregarCuentasaPagar"]')
   .wait(10)
   // -- end
   .click('#formPagoCuentas a[href^="javascript:enviar"]')
   .wait('fieldset')
   .evaluate(function () {
     return document.querySelector('.txt_detalle_boleta').innerHTML;
   })
   .end()
   .then(function (result) {
     console.log(result);
   })
   .catch(function (error) {
     console.error('Search failed:', error);
   });

How can I do it?

Prinzhorn · Accepted Answer · 2017-02-09 21:25:05Z

I know nothing about nightmare, but it looks like everything is queued until you call end and it just returns itself for chaining. So this should work

  var operations = nightmare.goto('https://www.servipag.com/');

  for(var i = 0; i < 4; i++) {
     operations = operations
        .select('select#servicios.txt_formulario', '29')
        .wait(200)
        .select('select#billers', '700')
        .insert('input#identificador','60957924')
        .click('#formPagoCuentas a[href^="javascript:AgregarCuentasaPagar"]')
        .wait(10);
  }

  operations
     .click('#formPagoCuentas a[href^="javascript:enviar"]')
     .wait('fieldset')
     .evaluate(function () {
       return document.querySelector('.txt_detalle_boleta').innerHTML;
     })
     .end()
     .then(function (result) {
       console.log(result);
     })
     .catch(function (error) {
       console.error('Search failed:', error);
     });

trincot · Accepted Answer · 2017-02-09 21:35:13Z

You could use reduce to keep the chain going:

Array(4).fill().reduce( acc =>
    acc.select('select#servicios.txt_formulario', '29')
       .wait(200)
       .select('select#billers', '700')
       .insert('input#identificador','60957924')
       .click('#formPagoCuentas a[href^="javascript:AgregarCuentasaPagar"]')
       .wait(10),
    nightmare.goto('https://www.servipag.com/') )
   .click('#formPagoCuentas a[href^="javascript:enviar"]')
   .wait('fieldset')
   .evaluate( _ => document.querySelector('.txt_detalle_boleta').innerHTML )
   .end()
   .then( result => console.log(result) )
   .catch( error => console.error('Search failed:', error) );

Note that the second argument to reduce provides the initial value before the "loop", so that is where nightmare.goto ... goes.

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