Read clipboard contents with InDesign

getClipboard.jsx

try {
	var pstwp = app.clipboardPreferences.preferStyledTextWhenPasting;
	app.clipboardPreferences.preferStyledTextWhenPasting = false;
	var doc = app.documents[0];
	var typoQ = doc.textPreferences.typographersQuotes;
	doc.textPreferences.typographersQuotes = false;

	var tf = doc.textFrames.add();
	tf.insertionPoints[-1].select();
	app.paste();

	var clipboard = tf.parentStory.contents;
	$.writeln(clipboard);
}
catch (e) {
	alert (e + " \nLine " + e.line);	
}
finally {
	app.clipboardPreferences.preferStyledTextWhenPasting = pstwp;
	doc.textPreferences.typographersQuotes = typoQ;
}

Ugly but works. Note the typographersQuotes, which are important for tabular/excel data.

found a better solution from harbs:

https://forums.adobe.com/thread/2022613

alert(GetClipboard());  
function GetClipboard(){  
    var clipboard;  
    if(File.fs == "Macintosh"){  
        var script = 'tell application "Finder"\nset clip to the clipboard\nend tell\nreturn clip';  
        clipboard = app.doScript (script,ScriptLanguage.APPLESCRIPT_LANGUAGE);  
    } else {  
        var script = 'Set objHTML = CreateObject("htmlfile")\r'+  
        'returnValue = objHTML.ParentWindow.ClipboardData.GetData("text")';  
        clipboard = app.doScript(script,ScriptLanguage.VISUAL_BASIC);  
    }  
    return clipboard;  
}