Making gulp write files synchronously before moving on to the next task

back to 2019: if some one come here with similar problem

In gulp 4.*, at least, gulp wait for promise to resolve but ignore the result. so... if you use async await pattern and return the result of gulp.src('...') you got a surprise. the task not wait for stream finish before it continue! somthing that can result to serious bug and waist of time. the solution is "promisify" gulp.src

example:

gulp.task( async function notWaitingTask(){
   // the return stream are ignored because function return promise not stream
   return gulp.src('file.js')
     .pipe(gulp.dest('new-location'))

})

gulp.task( async function waitingTask(){
   // the return stream are respect

   await promisifyStream(
     gulp.src('file.js')
      .pipe(gulp.dest('new-location'))
   )

})

function promisifyStream(stream) {
    return new Promise( res => stream.on('end',res));
}

The accepted answer is spot on, but as per https://github.com/gulpjs/gulp/issues/899, in the 3.x branch of gulp, you cannot do this with dependencies without a bit of extra special sauce:

var run = require('run-sequence');
var nodeunit = require('gulp-nodeunit');
var babel = require('gulp-babel');
var gulp = require('gulp');

/// Explicitly run items in order
gulp.task('default', function(callback) {
  run('scripts', 'tests', callback);
});

/// Run tests
gulp.task('tests', function() {
  return gulp.src('./build/**/*.tests.js').pipe(nodeunit());
});

// Compile ES6 scripts using bable
gulp.task('scripts', function() {
  return gulp.src('./src/**/*.js')
    .pipe(babel())
    .pipe(gulp.dest('./build'));
});

Notice specifically the use of the 'run-sequence' module to force the tasks to run one after another, as well.

(Without run, rm -rf build && gulp will result in OK: 0 assertions (0ms) because the tests task will not find the files created by the scripts task because it starts before the scripts task is completely resolved)

You need a return statement:

gulp.task('react', function(){
    return gulp.src(options.JSX_SOURCE)
        .pipe(react())
        .pipe(gulp.dest(options.JSX_DEST))
});

With this all my write operations are done before the next task processed.