Java: format Javascript code

Question

In my architecture Javascript code is generated in the server. A huge chunk of Javascript code is generated, stored in a java.lang.String and sent to the client side. I want to more easily debug the generated code (both the generation and how it runs).

Someone knows an easy way to format Javascript code?

Answer 1

It may be too late, but still.

I haven't found popular Java libraries for doing what you want; however, there are many javascript libraries for that (for example, js-beautify). You can save such library source code in resources of your application (you can get the code from one of cdn links, so you don't have to group and minify it manually), and then load it and invoke it with the Nashorn javascript engine.

Your code may look like this (roughly):

import javax.script.Invocable;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
import java.io.InputStreamReader;

public class JavascriptBeautifierForJava {

    // my javascript beautifier of choice
    private static final String BEAUTIFY_JS_RESOURCE = "beautify.js";

    // name of beautifier function
    private static final String BEAUTIFY_METHOD_NAME = "js_beautify";

    private final ScriptEngine engine;

    JavascriptBeautifierForJava() throws ScriptException {
        engine = new ScriptEngineManager().getEngineByName("nashorn");

        // this is needed to make self invoking function modules work
        // otherwise you won't be able to invoke your function
        engine.eval("var global = this;");
        engine.eval(new InputStreamReader(getClass().getClassLoader().getResourceAsStream(BEAUTIFY_JS_RESOURCE)));
    }

    public String beautify(String javascriptCode) throws ScriptException, NoSuchMethodException {
        return (String) ((Invocable) engine).invokeFunction(BEAUTIFY_METHOD_NAME, javascriptCode);
    }

    public static void main(String[] args) throws ScriptException, NoSuchMethodException {
        String unformattedJs = "var a = 1; b = 2; var user = { name : \n \"Andrew\"}";

        JavascriptBeautifierForJava javascriptBeautifierForJava = new JavascriptBeautifierForJava();
        String formattedJs = javascriptBeautifierForJava.beautify(unformattedJs);

        System.out.println(formattedJs);
        // will print out:
        //        var a = 1;
        //        b = 2;
        //        var user = {
        //            name: "Andrew"
        //        }
    }
}

If you're going to use this approach, make sure to reuse JavascriptBeautifier object, because it's not too effective to recreate one whenever you need to beautify code.

Answer 2

Two closely-related questions (possible duplicates):

• Command line JavaScript code beautifier that works on Windows and Linux
• https://stackoverflow.com/questions/6260431/pretty-print-javascript-using-java

Answer 3

May be late - but still :)

There is a pretty printer sample in jdk9 repo. This uses Nashorn Parser API (https://docs.oracle.com/javase/9/docs/api/jdk/nashorn/api/tree/Parser.html)

http://hg.openjdk.java.net/jdk9/dev/nashorn/file/17cc754c8936/samples/prettyprinter.js

Answer 4

The idea that comes to mind is manage your JavaScript output line by line (like a CodeLine class that has text and an indentation level) and when you're actually displaying this to the user and printing each line on a it's own line you can tab appropriately to format the code. It would require a custom class and probably something like an ArrayList<CodeLine>.

Answer 5

use firefox with addon firebug. You can add breakpoints in your generated javascript and do some step by step debugging.