Inner function doesn't know variable defined in outer scope. Why?

Question

I'm trying to navigate through pages of an online dictionary. Here is my code:

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

var links = [];
function goToLink(linkName){
    nightmare
        .goto(linkName)
        .evaluate( () => {
            var href = document.querySelector("span.next a").href;
            links.push(href)
            return href;
        })
        .then((href) => {
            goToLink(href);
        })
        .catch((error) => {
            console.error('Error:', error);
        });
}

goToLink("http://lexicon.quranic-research.net/data/01_a/000_!.html");

I'm getting Error: links is not defined. Links is clearly defined at var links = []; but the inner function doesn't know about it. What is going on here?

I could imagine that evaluate stringifies the argument and evals it ina different context. Edit: see github.com/segmentio/nightmare/issues/89 — Felix Kling
– Felix Kling, Commented Mar 12, 2017 at 16:41

Filip Koblański · Accepted Answer · 2017-03-15 09:35:47Z

1

The problem is that evaluate callback is called in a different context and doesn't see links. What you can try to do is to pass it like this:

(...)
.evaluate( links => {
    var href = document.querySelector("span.next a").href;
    links.push(href)
    return href;
}, links)
(...)

links are the parameter of the callback. You have to pass it as a second parameter in the evaluate function.

answered Mar 15, 2017 at 9:35

Filip Koblański

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1 Comment

Nick Manning Over a year ago

Ah you can pass an argument. Cool.

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