Intro.

Gulp 4 empowers developers to write tasks and combine tasks (in series or in parallel) in an imperative fashion:

gulp4.task( 'A', done => {done();} );
gulp4.task( 'B', done => {done();} );
gulp4.task( 'C', done => {done();} );

gulp4.task('default', gulp4.series('A', gulp4.parallel('B', 'C')));

This npm package provides developers an interface to combine gulp tasks in a declarative way as an alternative, it also calculates the overall task completion when an individual task finishes.

gulp4.task('default', parseGulpExpression('A | B & C'));

Installation:

$ npm install gulp4-expression

Usage:

• series: |
• parallel: &
• sub-expression parentheses: (...)

& has a higher precedence than |

// gulpfile.js

const gulp4 = require('gulp4');
const parseGulpExpression = require('gulp4-expression').parseGulpExpression;

// Register tasks
gulp4.task( 'A', done => {console.log('A'); setTimeout(done, 500);} );

gulp4.task( 'B', done => {console.log('B'); done()} );

gulp4.task( 'C', done => {console.log('C'); done()} );

gulp4.task( 'D', done => {console.log('D'); done()} );

gulp4.task( 'E', done => {console.log('E'); done()} );

gulp4.task( 'F', done => {console.log('F'); done()} );

gulp4.task( 'G', done => {console.log('G'); done()} );

gulp4.task( 'H', done => {console.log('H'); done()} );

// Combine tasks
gulp4.task('default', parseGulpExpression(
    '(A | B & C | D) & (E & F | G | H)'
));

$ gulp --tasks

# output
[14:56:13] └─┬ default
[14:56:13]   └─┬ <parallel>
[14:56:13]     ├─┬ <series>
[14:56:13]     │ ├── A (GulpExpressionNodeTask-1)
[14:56:13]     │ ├─┬ <parallel>
[14:56:13]     │ │ ├── B (GulpExpressionNodeTask-2)
[14:56:13]     │ │ └── C (GulpExpressionNodeTask-3)
[14:56:13]     │ └── D (GulpExpressionNodeTask-4)
[14:56:13]     └─┬ <series>
[14:56:13]       ├─┬ <parallel>
[14:56:13]       │ ├── E (GulpExpressionNodeTask-5)
[14:56:13]       │ └── F (GulpExpressionNodeTask-6)
[14:56:13]       ├── G (GulpExpressionNodeTask-7)
[14:56:13]       └── H (GulpExpressionNodeTask-8)

$ gulp --silent

# output
A
E
[14:56:38] progress: 8%
F
[14:56:38] progress: 17%
G
[14:56:38] progress: 33%
H
[14:56:38] progress: 50%
[14:56:38] progress: 67%
B
[14:56:38] progress: 75%
C
[14:56:38] progress: 83%
D
[14:56:38] progress: 100%

$ gulp

# output
[16:36:14] Starting 'default'...
[16:36:14] Starting 'A (GulpExpressionNodeTask-1)'...
A
[16:36:14] Starting 'E (GulpExpressionNodeTask-5)'...
[16:36:14] Starting 'F (GulpExpressionNodeTask-6)'...
E
[16:36:14] Finished 'E (GulpExpressionNodeTask-5)' after 688 μs
[16:36:14] progress: 8%
F
[16:36:14] Finished 'F (GulpExpressionNodeTask-6)' after 1.56 ms
[16:36:14] progress: 17%
[16:36:14] Starting 'G (GulpExpressionNodeTask-7)'...
G
[16:36:14] Finished 'G (GulpExpressionNodeTask-7)' after 318 μs
[16:36:14] progress: 33%
[16:36:14] Starting 'H (GulpExpressionNodeTask-8)'...
H
[16:36:14] Finished 'H (GulpExpressionNodeTask-8)' after 289 μs
[16:36:14] progress: 50%
[16:36:14] Finished 'A (GulpExpressionNodeTask-1)' after 508 ms
[16:36:14] progress: 67%
[16:36:14] Starting 'B (GulpExpressionNodeTask-2)'...
[16:36:14] Starting 'C (GulpExpressionNodeTask-3)'...
B
[16:36:14] Finished 'B (GulpExpressionNodeTask-2)' after 689 μs
[16:36:14] progress: 75%
C
[16:36:14] Finished 'C (GulpExpressionNodeTask-3)' after 838 μs
[16:36:14] progress: 83%
[16:36:14] Starting 'D (GulpExpressionNodeTask-4)'...
D
[16:36:14] Finished 'D (GulpExpressionNodeTask-4)' after 409 μs
[16:36:14] progress: 100%
[16:36:14] Finished 'default' after 513 ms