johntitus/node-horseman

Add support for polyfilling missing PhantomJS JavaScript features

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#230 opened on Oct 27, 2016

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enhancementhelp wanted

Description

PhantomJS does not support some features that websites expect it to. It would be nice for horseman to have built-in support for polyfilling these features.

Here is a way I came up with for polyfilling externally with Polyfill.io, for reference. It is somewhat gross, so if someone comes up with a better way that's great.

var Horseman = require('node-horseman');
var POLYURL = 'https://cdn.polyfill.io/v2/polyfill.min.js';

var horseman = new Horseman();

horseman
    .userAgent()
    .then(function(useragent) { // Get Polyfill based on real UserAgent
        return this.download(POLYURL + '?ua=' + useragent);
    })
    .then(function(polyfill) {
        // Make polyfill into function
        var polyfun = new Function(polyfill);
        // Wrap function in evaluateJavaScript
        var onInit = new Function(
            'console.log("onInitialized");' +
            'page.evaluateJavaScript(' + polyfun.toString() + ')'
        );
        // Call before page loads
        return this.at('initialized', onInit);
    })
    /* Do horseman stuff now */

Assistance/contribution would be greatly appreciated.

Contributor guide

Tech stack
javascriptnodejs
Domain
tooling
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
JavaScriptNode.jsPhantomJS basicsPolyfill concepts
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
55
Research direction
The issue requests a built in polyfilling mechanism. A suggested approach uses the 'initialized' event and page.evaluateJavaScript. Newcomers should examine the Horseman source code to understand the event lifecycle and how to inject scripts before page load. They may also research other polyfill options like polyfill.io or custom polyfills.