How to inject variable value into JS file from GULP

Question

Hopefully this is a quick question.

What I'm trying to do is to add a timestamp into a Javascript object in a JS file while the file is being built with GULP. Basically, in "file.js", I have an object where I would like to have object.timeStamp that equals the time of the GULP build.

I am currently adding a timestamp to the top of the file using gulp-header, but I have been asked to add the timestamp to a property in the object.

My thought was to inject the value from GULP, but all of the injection plugins I have found so far are for injecting contents of one file into the target file.

Any help would be greatly appreciated.

Answer 1

Are you using any kind of modules? ES6 modules, AMD, CommonJS, ...?

If so, you can generate a config module with Gulp where you can inject any variable you want. It would look something like this:

config.tmpl.js

module.exports = <%= config %>

config gulp task

var gulp = require('gulp');
var template = require('gulp-template');
var rename = require('gulp-rename');

gulp.task('config', function() {
  return gulp.src('path/to/config.tmpl.js')
    .pipe(template({config: JSON.stringify({
      timeStamp: new Date()
    })}))
    .pipe(rename('config.js'))
    .pipe(gulp.dest('path/to/config.js'));
});

and finally, in your JS file

var config = require('path/to/config.js');

var object = {
  timeStamp: config.timeStamp
}

Answer 2

OK, so I figured out a workaround that gets me where I want to be. The first this is using the gulp-header to insert a variable declaration into my Javascript file using this code:

In GULP:

    var d = new Date();
    .pipe(header("var timeStamp = '" + d +"';"))

Then, in my Javascript file, I set up a property in the object that is a function, and sets the timeStamp property I was looking for by getting the value from the timeStamp variable injected above using the gulp-header, like this:

In the JS File, the header functionality inserts this:

    var timeStamp = 'Tue Dec 08 2015 15:15:11 GMT-0800 (PST)';

And then my function, in the JS Object is simply this:

   ts: function(){
    object.timeStamp = timeStamp;
   },

Which, when called, runs and sets the timestamp inside of the object.

It seems like there should be an easier way to do this, but for now, this is working.

If you have any ideas on making it better, I would love to hear them!