Prevent errors from breaking / crashing gulp watch

Question

Your swallowError function should look like this:

function swallowError (error) {

  // If you want details of the error in the console
  console.log(error.toString())

  this.emit('end')
}

I think you have to bind this function on the error event of the task that was falling, not the watch task, because that's not where comes the problem, you should set this error callback on each task that may fail, like plugins that breaks when you have missed a ; or something else, to prevent watch task to stop.

Examples :

gulp.task('all', function () {
  gulp.src('./app/script/*.coffee')
    .pipe(coffee({ bare: true }))
    .on('error', swallowError)
    .pipe(gulp.dest('./public/js'))

  gulp.src('css/*.scss')
    .pipe(sass({ compass: true }))
    .on('error', swallowError)
    .pipe(cssmin())
    .pipe(gulp.dest('dist'))
})

Alternately, if you don't mind to include another module, you can use the log function of gulp-util to keep you from declare an extra function in your gulpfile:

.on('error', gutil.log)

---

But I may recommend having a look at the awesome gulp-plumber plugin, which is used to remove the onerror handler of the error event, causing the break of the streams. It's very simple to use and it stops you from catch all the tasks that may fail.

gulp.src('./app/script/*.coffee')
  .pipe(plumber())
  .pipe(coffee({ bare: true }))
  .pipe(gulp.dest('./public/js'))

More info about this on this article by the creator of the concerned plugin.

The above examples didn't work for me. The following did though:

var plumber = require('gulp-plumber');
var liveReload = require('gulp-livereload');
var gutil = require('gulp-util');
var plumber = require('gulp-plumber');
var compass = require('gulp-compass');
var rename = require('gulp-rename');
var minifycss = require('gulp-minify-css');
var notify = require('gulp-notify');

gulp.task('styles', function () {
    //only process main.scss which imports all other required styles - including vendor files.
    return gulp.src('./assets/scss/main.scss')
            .pipe(plumber(function (error) {
                gutil.log(error.message);
                this.emit('end');
            }))
            .pipe(compass({
                config_file: './config.rb',
                css: './css'
                , sass: './assets/scss'
            }))
            //minify files
            .pipe(rename({suffix: '.min'}))
            .pipe(minifycss())

            //output
            .pipe(gulp.dest('./css'))
            .pipe(notify({message: 'Styles task complete'}));
});

gulp.task('watch', function () {
    liveReload.listen();
    gulp.watch('assets/scss/**/*.scss', ['styles']);
});

With one format of files

(ex: *.coffee only)

If you want to work only with one format of files, then gulp-plumber is your solution.

For example rich handled errors and warning for coffeescripting:

gulp.task('scripts', function() {
  return gulp.src(['assets/scripts/**/*.coffee'])
    .pipe(plumber())
    .pipe(coffeelint())
    .pipe(coffeelint.reporter())
    .pipe(lintThreshold(10, 0, lintThresholdHandler))
    .pipe(coffee({
      bare: true
    }))
    .on('error', swallowError)
    .pipe(concat('application.js'))
    .pipe(gulp.dest('dist/scripts'))
    .pipe(rename({ suffix: '.min' }))
    .pipe(uglify())
    .pipe(gulp.dest('dist/scripts'))
    .pipe(notify({ message: 'Scripts task complete' }));
});

With multiple types of file formats

(ex: *.coffee and *.js at same time)

But if you won't to work with multiple types of file formats (for example: *.js and *.coffee), than i will post my solution.

I will just post a self explanatory code over here, with some description before.

gulp.task('scripts', function() {
  // plumber don't fetch errors inside gulpif(.., coffee(...)) while in watch process
  return gulp.src(['assets/scripts/**/*.js', 'assets/scripts/**/*.coffee'])
    .pipe(plumber())
    .pipe(gulpif(/[.]coffee$/, coffeelint()))
    .pipe(coffeelint.reporter())
    .pipe(lintThreshold(10, 0, lintThresholdHandler))
    .pipe(gulpif(/[.]coffee$/, coffee({ // if some error occurs on this step, plumber won't catch it
      bare: true
    })))
    .on('error', swallowError)
    .pipe(concat('application.js'))
    .pipe(gulp.dest('dist/scripts'))
    .pipe(rename({ suffix: '.min' }))
    .pipe(uglify())
    .pipe(gulp.dest('dist/scripts'))
    .pipe(notify({ message: 'Scripts task complete' }));
});

I faced the issue with gulp-plumber and gulp-if using gulp.watch(...

See related issue here: https://github.com/floatdrop/gulp-plumber/issues/23

So the best option for me was:

• Each part as file, and concatenate after. Create multiple tasks that can process each part in separate file (like grunt does), and concatenate them
• Each part as stream, and merge streams after. Merge two streams using merge-stream (that was made from event-stream) into one and continue the job (i tried that first, and it work fine for me, so it is faster solution than previous one)

---

Each part as stream, and merge streams after

Her is the main part of my code:

gulp.task('scripts', function() {
  coffeed = gulp.src(['assets/scripts/**/*.coffee'])
    .pipe(plumber())
    .pipe(coffeelint())
    .pipe(coffeelint.reporter())
    .pipe(lintThreshold(10, 0, lintThresholdHandler))
    .pipe(coffee({
      bare: true
    }))
    .on('error', swallowError);

  jsfiles = gulp.src(['assets/scripts/**/*.js']);

  return merge([jsfiles, coffeed])
    .pipe(concat('application.js'))
    .pipe(gulp.dest('dist/scripts'))
    .pipe(rename({ suffix: '.min' }))
    .pipe(uglify())
    .pipe(gulp.dest('dist/scripts'))
    .pipe(notify({ message: 'Scripts task complete' }));
});

---

Each part as file, and concatenate after

If to separate this into parts, then in each part there should be a result file created. For ex.:

gulp.task('scripts-coffee', function() {

  return gulp.src(['assets/scripts/**/*.coffee'])
    .pipe(plumber())
    .pipe(coffeelint())
    .pipe(coffeelint.reporter())
    .pipe(lintThreshold(10, 0, lintThresholdHandler))
    .pipe(coffee({
      bare: true
    }))
    .on('error', swallowError)
    .pipe(concat('application-coffee.js'))
    .pipe(gulp.dest('dist/scripts'));

});

gulp.task('scripts-js', function() {

  return gulp.src(['assets/scripts/**/*.js'])
    .pipe(concat('application-coffee.js'))
    .pipe(gulp.dest('dist/scripts'));

});

gulp.task('scripts', ['scripts-js', 'scripts-coffee'], function() {

  var re = gulp.src([
    'dist/scripts/application-js.js', 'dist/scripts/application-coffee.js'
  ])
    .pipe(concat('application.js'))
    .pipe(gulp.dest('dist/scripts'))
    .pipe(rename({ suffix: '.min' }))
    .pipe(uglify())
    .pipe(gulp.dest('dist/scripts'))
    .pipe(notify({ message: 'Scripts task complete' }));

  del(['dist/scripts/application-js.js', 'dist/scripts/application-coffee.js']);

  return re;

});

P.S.:

Here node modules and functions that were used:

// Load plugins
var gulp = require('gulp'),
    uglify = require('gulp-uglify'),
    rename = require('gulp-rename'),
    concat = require('gulp-concat'),
    notify = require('gulp-notify'),
    plumber = require('gulp-plumber'),
    merge = require('ordered-merge-stream'),
    replace = require('gulp-replace'),
    del = require('del'),
    gulpif = require('gulp-if'),
    gulputil = require('gulp-util'),
    coffee = require('gulp-coffee'),
    coffeelint = require('gulp-coffeelint),
    lintThreshold = require('gulp-coffeelint-threshold');

var lintThresholdHandler = function(numberOfWarnings, numberOfErrors) {
  var msg;
  gulputil.beep();
  msg = 'CoffeeLint failure; see above. Warning count: ';
  msg += numberOfWarnings;
  msg += '. Error count: ' + numberOfErrors + '.';
  gulputil.log(msg);
};
var swallowError = function(err) {
  gulputil.log(err.toString());
  this.emit('end');
};

I like to use gulp plumber because it can add a global listener to a task and have a meaningful message displayed.

var plumber = require('gulp-plumber');

gulp.task('compile-scss', function () {
    gulp.src('scss/main.scss')
        .pipe(plumber())
        .pipe(sass())
        .pipe(autoprefixer())
        .pipe(cssnano())
        .pipe(gulp.dest('css/'));
});

Reference : https://scotch.io/tutorials/prevent-errors-from-crashing-gulp-watch