There is a website that contains a page with a list of 25 entries, where each entry is a link to a page containing some information that I need. I want get to the listing page and then: 1) click on link to first entry 2) retrieve all the html 3) click back to the listing page (there is a button for this) 4) repeat for every other listing
I would also like to do this as efficiently as possible which I've been told means leveraging promises. Here's my code sketch, which doesn't work:
var Nightmare = require('nightmare');
var nightmare = Nightmare({ openDevTools: true, show: true })
var Xray = require('x-ray');
var x = Xray();
var resultArr = [];
nightmare
.goto(hidTestURL)
.wait(2500)
.click('input[name="propertySearchOptions:advanced"]') //start navigating to listing page
.wait(2500)
.type('input[name="propertySearchOptions:streetName"]', 'Main')
.wait(2500)
.select('select[name="propertySearchOptions:recordsPerPage"]', '25')
.wait(2500)
.click('input[name="propertySearchOptions:search"]') //at listing page
.wait(2500)
.then(function(){
nightmare
.click('a[href^="Property.aspx?prop_id=228645"]') //first entry
.evaluate(function(){ //retrieve info
var resultArr = [];
resultArr.push(document.querySelector('html').innerHTML);
})
})
nightmare
.click('a[id="propertyHeading_searchResults"]') //return to listing page
.evaluate(function(){
return resultArr.push(document.querySelector('html').innerHTML); retrieve listing page info to show that it returned.
})
.then(function (resultArr) {
console.log('resultArr', resultArr);
x(resultArr[1], 'body@html') //output listing page html
.write('results.json');
})
This gets as far as the listing page, and then does not proceed any further. I also tried the same code, but with return nightmare for every use of nightmare except the first one. I'd seen some examples that used return, but when I did this, the code threw an error.
I also tried not including the third nightmare (the one after the blank space), and instead trying to continue the old nightmare instance by going straight to the .click(), but this also threw an error.
I clearly need some help with the syntax and semantics of nightmare, but there is not much documentation online besides an API listing. Does anyone know how I can make this work?
First, calling Nightmare like you have it - broken into two chains - is probably not going to do what you want. (This comment thread is a good - albeit long - primer.) Memory serving, actions from the second chain will be queued immediately after the first, resulting in (probably) undesirable behavior. You said you had it written slightly differently - I'd be curious to see it, it sounds like it may have been a little closer.
Second, you're trying to lift resultArr in .evaluate(), which isn't possible. The function passed to .evaluate() is stringified and reconstituted inside of Electron - meaning that you'll lose the ambient context around the function. This example in nightmare-examples goes into a little more depth, if you're curious.
Third, and maybe this is a typo or me misunderstanding intent: your href selector uses the starts-with (^=) operator, is that intentional? Should that be an ends-with ($=)?
Fourth, looping over asynchronous operations is tricky. I get the impression that may also be a stumbling block?
With all of that in mind, let's take a look at modifying your original script. Admittedly untested, as I don't have access to your testing URL, so this is a bit from the hip:
var Nightmare = require('nightmare');
var nightmare = Nightmare({ openDevTools: true, show: true })
var Xray = require('x-ray');
var x = Xray();
nightmare
.goto(hidTestURL)
.wait(2500)
.click('input[name="propertySearchOptions:advanced"]') //start navigating to listing page
.wait(2500)
.type('input[name="propertySearchOptions:streetName"]', 'Main')
.wait(2500)
.select('select[name="propertySearchOptions:recordsPerPage"]', '25')
.wait(2500)
.click('input[name="propertySearchOptions:search"]') //at listing page
.wait(2500)
.evaluate(function(){
//using `Array.from` as the DOMList is not an array, but an array-like, sort of like `arguments`
//planning on using `Array.map()` in a moment
return Array.from(
//give me all of the elements where the href contains 'Property.aspx'
document.querySelectorAll('a[href*="Property.aspx"]'))
//pull the target hrefs for those anchors
.map(a => a.href);
})
.then(function(hrefs){
//here, there are two options:
// 1. you could navigate to each link, get the information you need, then navigate back, or
// 2. you could navigate straight to each link and get the information you need.
//I'm going to go with #1 as that's how it was in your original script.
//here, we're going to use the vanilla JS way of executing a series of promises in a sequence.
//for every href in hrefs,
return hrefs.reduce(function(accumulator, href){
//return the accumulated promise results, followed by...
return accumulator.then(function(results){
return nightmare
//click on the href
.click('a[href="'+href+'"]')
//get the html
.evaluate(function(){
return document.querySelector('html').innerHTML;
})
//add the result to the results
.then(function(html){
results.push(html);
return results;
})
.then(function(results){
//click on the search result link to go back to the search result page
return nightmare
.click('a[id="propertyHeading_searchResults"]')
.then(function() {
//make sure the results are returned
return results;
});
})
});
}, Promise.resolve([])) //kick off the reduce with a promise that resolves an empty array
})
.then(function (resultArr) {
//if I haven't made a mistake above with the `Array.reduce`, `resultArr` should now contain all of your links' results
console.log('resultArr', resultArr);
x(resultArr[1], 'body@html') //output listing page html
.write('results.json');
});
Hopefully that's enough to get you started.
来源：https://stackoverflow.com/questions/38772060/moving-between-pages-and-scraping-as-i-go-with-nightmare