Gulp - how to delete build directory before running other tasks - gulp

Question

I got this Gulp file where I'm running various tasks.
I would like to delete the contents of my build directory before running any other tasks but can't work out how to do this.
I've tried lots of various ways I found when searching for a solution to this but can't get it to work.
Here is my Gulp file:
// List required plugins
var gulp = require('gulp'),
del = require('del'),
uglify = require('gulp-uglify'),
postcss = require('gulp-postcss'),
lost = require('lost'),
nano = require('gulp-cssnano'),
sourcemaps = require('gulp-sourcemaps'),
autoprefixer = require('autoprefixer'),
mqpacker = require('css-mqpacker'),
mixins = require('postcss-mixins'), // Must go before other plugins in the PostCSS task
nested = require('postcss-nested'),
vars = require('postcss-simple-vars'),
partials = require('postcss-import'),
plumber = require('gulp-plumber'),
gutil = require('gulp-util'),
imagemin = require('gulp-imagemin'),
pngquant = require('imagemin-pngquant'),
browserSync = require('browser-sync').create();
// Config - Paths and other config
var src = {
cssDir: 'src/css/**/*.css',
jsDir: 'src/js/**/*.js',
imgDir: 'src/img/*',
svgDir: 'src/img/svg/**/*.svg',
htmlDir: 'src/**/*.html',
srcDir: 'src/',
},
build = {
buildDir: 'build/',
cssDir: 'build/assets/css/',
htmlDir: 'build/**/*.html',
jsDir: 'build/assets/js/',
imgDir: 'build/assets/img/',
},
options = {
autoprefix: { browsers: ['last 2 versions'] },
imagemin: { optimizationLevel: 7, progressive: true, interlaced: true, svgoPlugins: [ {removeViewBox: false}, {cleanupIDs: false} ], use: [pngquant()] },
port: '80',
};
// Error handling function
// Thanks to https://cameronspear.com/blog/how-to-handle-gulp-watch-errors-with-plumber/
var onError = function(err) {
gutil.beep();
console.log(err);
this.emit('end');
}
// Clean task
gulp.task('clean:build', function () {
return del([
build.buildDir,
]);
});
// Copy HTML to Build
gulp.task('html', function () {
return gulp.src(src.htmlDir)
.pipe(plumber({
errorHandler: onError
}))
.pipe(gulp.dest(build.buildDir))
.pipe(browserSync.stream());
});
// BrowserSync Server + watching files for changes
gulp.task('server', function() {
browserSync.init({
server: {
baseDir: build.buildDir
},
port: options.port,
});
});
// PostCSS Task
gulp.task('css', function () {
var processors = [
partials(),
lost(),
autoprefixer({ browsers: ['last 2 version'] }),
mixins(),
nested(),
vars(),
mqpacker(), // Make sure mqpacker is last!
];
return gulp.src(src.cssDir)
.pipe(plumber({
errorHandler: onError
}))
.pipe(sourcemaps.init())
.pipe(postcss(processors))
//.pipe(nano()) - Disable minification during development
.pipe(sourcemaps.write('.'))
.pipe(gulp.dest(build.cssDir))
.pipe(browserSync.stream());
});
// JS Task
gulp.task('compressJS', function() {
return gulp.src(src.jsDir)
.pipe(plumber({
errorHandler: onError
}))
.pipe(uglify())
.pipe(gulp.dest(build.jsDir))
.pipe(browserSync.stream());
});
// Image Task
gulp.task('imagemin', function() {
return gulp.src(src.imgDir)
.pipe(plumber({
errorHandler: onError
}))
.pipe(imagemin(
options.imagemin
))
.pipe(gulp.dest(build.imgDir))
.pipe(browserSync.stream());
});
gulp.task('watch', function () {
gulp.watch(src.cssDir, ['css']);
gulp.watch(src.jsDir, ['compressJS']);
gulp.watch(src.htmlDir, ['html']);
gulp.watch(src.imgDir, ['imagemin']);
});
gulp.task('default', ['html', 'imagemin', 'compressJS', 'server', 'watch']);
How should I do to run the task clean:build before any other tasks but only run it once. Or is there a better way of cleaning out files before running a build?
Thanks!!

Answer 1

Have your tasks depend on your clean task:
gulp.task('html', ['clean:build'], function() { ... })

Answer 2

this is how i do it.
var del = require('del') ;
gulp.task('delete-build-folder', function(cb) {
return del([config.buildDir], cb);
});
gulp.task('default', ['delete-build-folder'], function() {
console.log('building.....');
gulp.start('copy-html', 'copy-html-views');
});