Using Selenium to determine the visibility of elements for Print media

css, selenium-webdriver

Solution

I've managed to write a script that does just what you want: it hides screen-only styles and sets print-only styles to be screen-only.

You need to inject the following JavaScript with Selenium:

(function pretendToBeAPrinter() {
    //For looking up if something is in the media list
    function hasMedia(list, media) {
        if (!list) return false;

        var i = list.length;
        while (i--) {
            if (list[i] === media) {
                return true;
            }
        }
        return false;
    }

    //Loop though all stylesheets
    for (var styleSheetNo = 0; styleSheetNo < document.styleSheets.length; styleSheetNo++) {
        //Current stylesheet
        var styleSheet = document.styleSheets[styleSheetNo];

        //Output debug information
        console.info("Stylesheet #" + styleSheetNo + ":");
        console.log(styleSheet);

        //First, check if any media queries have been defined on the <style> / <link> tag

        //Disable screen-only sheets
        if (hasMedia(styleSheet.media, "screen") && !hasMedia(styleSheet.media, "print")) {
            styleSheet.disabled = true;
        }

        //Display "print" stylesheets
        if (!hasMedia(styleSheet.media, "screen") && hasMedia(styleSheet.media, "print")) {
            //Add "screen" media to show on screen
            styleSheet.media.appendMedium("screen");
        }

        // Get the CSS rules in a cross-browser compatible way
        var rules;
        try {
            rules = styleSheet.cssRules;
        } catch (error) {
            console.log(error);
        }

        try {
          rules = styleSheet.rules;
        } catch (error) {
          console.log(error);
        }

        // Handle cases where styleSheet.rules is null
        if (!rules) {
            continue;
        }

        //Second, loop through all the rules in a stylesheet
        for (var ruleNo = 0; ruleNo < rules.length; ruleNo++) {
            //Current rule
            var rule = rules[ruleNo];

            //Hide screen-only rules
            if (hasMedia(rule.media, "screen") && !hasMedia(rule.media, "print")) {
                //Rule.disabled doesn't work here, so we remove the "screen" rule and add the "print" rule so it isn't shown
                console.info('Rule.media:');
                console.log(rule.media)
                rule.media.appendMedium(':not(screen)');
                rule.media.deleteMedium('screen');
                console.info('Rule.media after tampering:');
                console.log(rule.media)
            }

            //Display "print" rules
            if (!hasMedia(rule.media, "screen") && hasMedia(rule.media, "print")) {
                //Add "screen" media to show on screen
                rule.media.appendMedium("screen");
            }
        }
    }
})()

You can see it in action at JSFiddle.

Bookmarklet

You can also install it as a bookmarklet.

More information:

- About `mediaList`

- About `document.styleSheets`

Note: I've only tested this in Google Chrome and Mozilla Firefox. It may or may not work in other browsers.

Problem

Original source