How to create a gulp file with reusable functions - Multiple Watch points & Multiple Output destinations

Question

Goal is to use this Gulp file to execute 'n' number of different source & destinations.

How can we pass the arguments(source, destination) so that the CSS-Generator task is accepting those source & destinations and giving out the separate output files.

var gulp = require("gulp"),
  sass = require("gulp-sass"),
  postcss = require("gulp-postcss"),
  autoprefixer = require("autoprefixer"),
  cssnano = require("cssnano");

var paths = {
  styles: {
    src1: "scss/slider-one/index.scss",
    src2: "scss/slider-two/index.scss"

    dest1: "slider-one",
    dest2: "slider-two"
  }
};

function style1() {
  return (
    gulp
     .src(paths.styles.src1)
     .pipe(sass())
     .on("error", sass.logError)
     .pipe(postcss([autoprefixer(), cssnano()]))
     .pipe(gulp.dest(paths.styles.dest1))
  );
 }

 exports.style1 = style1;

 function style2() {
  return (
    gulp
      .src(paths.styles.src2)
      .pipe(sass())
      .on("error", sass.logError)
      .pipe(postcss([autoprefixer(), cssnano()]))
      .pipe(gulp.dest(paths.styles.dest2))
  );
 }

 exports.style2 = style2;

 function watch() {

   style1();
   style2();

   gulp.watch("scss/slider-one/*.scss", style1);
   gulp.watch("scss/slider-two/*.scss", style2);
  }

  exports.watch = watch

Answer 1

Your source is scss/slider-one/index.scss & destination is slider-one and watch is scss/slider-one/*.scss.

slider-one is common in source, destination & watch.

So you can define the paths array as ["slider-one","slider-two"]

And you are calling the style1 & style2 as the callback of watch function. So you can club that and define that in one function.

And call that function inside for loop with parameters (source,destination,watch).

Full Code:

var gulp = require("gulp"),
 sass = require("gulp-sass"),
 postcss = require("gulp-postcss"),
 autoprefixer = require("autoprefixer"),
 cssnano = require("cssnano");

function runGulpSass(src,dest,watch) {
 gulp.watch(watch, function() {
   return gulp.src(src)
          .pipe(sass())
          .on("error", sass.logError)
          .pipe(postcss([autoprefixer(), cssnano()]))
          .pipe(gulp.dest(dest))
 });
}

exports.runGulpSass = runGulpSass;

function startGulp() {
 var paths = ["slider-one","slider-two"];
 for(var i=0;i<paths.length;i++) {
   runGulpSass("scss/"+paths[i]+"/index.scss",paths[i],"scss/"+paths[i]+"/*.scss")
 }
}

exports.watch = startGulp

[Edit] If there is no common value in source, destination & watch :

Define the paths array like this :

var paths = [
    ["scss/slider-one/index.scss","css/slider-one","slider-one/*.scss"],
    ["scss/slider-two/index.scss","css/slider-two","slider-two/*.scss"]
];

And set the runGulpSass function parameter like this :

runGulpSass(paths[i][0],paths[i][1],paths[i][2])