Prepend and append single value with stream

[ORESoftware]

This regards Node.js versions >= 4.0.0

Say I have a file with this content:

var foo = 'bar';

I want to read this file in, wrap it in a function and replace "bar" with "star"

something like this =>

Test.create(function(){
   var foo = 'star';
});

so I can use a transform stream (replace stream to replace bar with star) like so:

fs.createReadStream(<file1>)
.pipe(new ReplaceStream('bar','star')).pipe(fs.createWriteStream(<file2>));

but my question is - what might be the recommended way to wrap the whole thing in a function? Is there a streamlined way that someone can think of do that?

Something like:

const writable = fs.createWriteStream(<file2>)
writable.write('Test.create(function(){');
fs.createReadStream(<file1>, {end:false})
.pipe(new ReplaceStream('bar','star')).pipe(writable, {end:false});
writable.end('})');

is that about right?

[ORESoftware]

The problem with my code above, is I still get a "write after end" error...even though I have declared {end:false} in two places. Why would that be?

the error is caused by this line:
writable.end('})');

[ORESoftware]

I used this, which seems to work:

    const writable = fs.createWriteStream(fileObj.mappedPath);
    writable.write("\nconst suman = require('suman');\n");
    writable.write("const Test = suman.init(module);\n\n");
    writable.write('Test.create(function(describe, it, before, after, beforeEach, afterEach){\n');

    fs.createReadStream(fileObj.originalPath)
        .pipe(new ReplaceStream('bar','star'))
        .pipe(writable)
        .once('finish', function () {
          fs.appendFile(fileObj.mappedPath, '\n\n});\n', cb);
        });

not that thrilled with having to use fs.appendFile at the end, but it should work, I think.