How do I mix promises and pipe in gulp? - promise

Question

In my project I compile multiple bundles from source files in nested directories using rollup.
I had a gulpfile with the following code, which worked fine:
function build_app_js(file, name) {
return gulp.src(file)
.pipe(sourcemaps.init())
.pipe(rollup({format:'iife'}))
.pipe(terser())
.pipe(rename(name + '.js'))
.pipe(rename({suffix: '.min'}))
.pipe(sourcemaps.write())
.pipe(gulp.dest(js_apps_dir))
}
// call the above for multiple sets of file+app_name
But then I changed one of the dependencies in my ES6 code which I accessed by relative path into an npm package, so it is now in node_modules. Rollup needs a plugin to resolve this, so I changed the above to this:
.pipe(rollup({plugins: [resolveNodeModules()], format:'iife'}))
However this simply does not work.
I consulted rollup's docs on gulp, and adapted the example to my case, so it now looks like this:
function build_app_js(file, name) {
return rollup.rollup({
input: file,
plugins: [
resolveNodeModules()
]
}).then(bundle => {
return bundle.write({
file: js_apps_dir + '/' + name + '.js',
format: 'iife',
sourcemap: true
});
});
}
This works, but has no minification step, and I don't know how to add one.
More generally, this is a totally different paradigm from using pipe(), and I do not know how to make both work together.
Do I try to add minification in the Promise syntax, or do I wrap the Promise function in such a way that I can use it with pipe?

Answer 1

Answering own question after 8 days.
Minification can be achieved via rollup plugins, such as rollup-plugin-terser.
You just need to be careful with how you import them:
var rollup = require('rollup');
var resolveNodeModules = require('rollup-plugin-node-resolve');
//var terser = require('rollup-plugin-terser'); // WRONG
var {terser} = require('rollup-plugin-terser'); // CORRECT
function build_app_js(file, name) {
return rollup.rollup({
input: file,
plugins: [
resolveNodeModules(),
terser()
]
}).then(bundle => {
return bundle.write({
file: js_apps_dir + '/' + name + '.js',
format: 'iife',
sourcemap: true
});
});
}
If you import it the wrong way, you will get a terser() is not a function type error, which is because it will have imported terser as a module.
It's a bit annoying that different rollup-plugins can't be imported the same way, but hey.