Quick Start

SlimerJS executes your script in the context of a blank window (that you cannot see). So you have a document object, a window object, even if it is not really useful. You have other objects that allow you to do many tasks.

Hello World

Since SlimerJS is called from the command line, the first thing you could do in your script is to print something in the terminal. You do it with the console object, as in any web page.

console.log("Hello Slimer!");

Store this script into a hello.js file and execute it:

slimerjs hello.js

You’ll see a little window opening and the “hello” message in the terminal. And that’s all. Contrary to PhantomJS, SlimerJS is not headless by default, this is why you see this window. But if you are using Firefox 56 or higher, you can add --headless on the command line to not see windows. Or with older Firefoxes, on Linux, you can use the tool xvfb to hide all windows opened by your script. See the documentation about it.

You see that you have to close the window by yourself. To close it automatically, call slimer.exit() (or phantom.exit() to be compatible with PhantomJS), at the end of your script.

console.log("Hello Slimer!");
slimer.exit();

Loading a module

All components and libraries provided by SlimerJS are stored in modules. It follows the CommonJS module standard. (No support of ES6 module yet). A module is a javascript file that “exports” a number of functions to the caller script. To “import” this functions in your scripts, you have to use the require() function. It accepts the module name in parameter, and returns an object.

var webpageModule = require("webpage");

The result of require, here stored into webpageModule, is an object that have all exported functions of the module.

SlimerJS has modules almost identical to those provided by PhantomJS (webpage, fs, webserver, system) but it has also many other modules from the Mozilla Addons SDK which is included into the SlimerJS package.

Opening a web page

The main goal of SlimerJS is to open a web page and to manipulate it or to extract data from it. You have a dedicated module for that, “webpage”.

This module provides only one function, create() that creates a webpage object.

var page = require("webpage").create();
page.open("http://slimerjs.org")
    .then(function(status){
         if (status == "success") {
             console.log("The title of the page is: "+ page.title);
         }
         else {
             console.log("Sorry, the page is not loaded");
         }
         page.close();
         phantom.exit();
    })

In SlimerJS, the open() method of the webpage object returns a “promise”, a kind of object that allows to execute asynchronous tasks one after an other (you can chain easily several page loading with this object). In our example, the webpage object load the page at the given URL, and when it is loaded, it executes the “then” step. Here we check the result of the loading, and if it is ok, we display the page title.

You can use also the same API of PhantomJS (It doesn’t return a promise): give a callback function to open():

var page = require("webpage").create();
page.open("http://slimerjs.org", function(status){
     if (status == "success") {
         console.log("The title of the page is: "+ page.title);
     }
     else {
         console.log("Sorry, the page is not loaded");
     }
     page.close();
     phantom.exit();
})

Code Evaluation

Once a web page is opened, you may need to execute a javascript function into the context of the web page, in order to retrieve data or to manipulate the page content.

This function must not call functions or use variables, of your script. It will not have access to them when it will be executed. The function can return a value: it should be only simple javascript values : array, number, string or literal object. But not objects like DOM objects...

To execute such function, use the evaluate() method of the web page object:

var page = require('webpage').create();
page.open("http://slimerjs.org", function (status) {
    var mainTitle = page.evaluate(function () {
        console.log('message from the web page');
        return document.querySelector("h1").textContent;
    });
    console.log('First title of the page is ' + mainTitle);
    slimer.exit()
});

You may notice that you don’t see the message “message from the web page”. Any console messages sent from the web page are not displayed by default. You need to give a callback on the property onConsoleMessage, that will do it:

var page = require('webpage').create();
page.onConsoleMessage = function (msg) {
    console.log(msg);
};
page.open("http://slimerjs.org", function (status) {
    var mainTitle = page.evaluate(function () {
        console.log('message from the web page');
        return document.querySelector("h1").textContent;
    });
    console.log('First title of the page is ' + mainTitle);
    slimer.exit()
});

Taking screenshots

You can capture the page rendering and store it into an image, with the render() method:

var page = require('webpage').create();
page.open("http://slimerjs.org", function (status) {
    page.viewportSize = { width:1024, height:768 };
    page.render('screenshot.png')
});

viewportSize allows you to set the window size.

Network monitoring

You can listen all HTTP steps made during a page loading. You have several callback you can give.

To listen the full loading of the page (when all of its resources are loaded), you may set the onLoadStarted callback to know when the loading starts, and onLoadFinished when the page is fully loaded.

var page = require('webpage').create();
var startTime;
page.onLoadStarted = function () {
    startTime = new Date()
};
page.onLoadFinished = function (status) {
    if (status == "success") {
        var endTime = new Date()
        console.log('The page is loaded in '+ ((endTime - startTime)/1000)+ " seconds" );
    }
    else
        console.log("The loading has failed");
};
page.open(url);

This example displays the time spent to load the page.

You can also listen all HTTP requests and responses with callbacks onResourceRequested and onResourceReceived.

More informations

The documentation is not yet complete. You can read the documentation of PhantomJS to know more about the API.