Gulp custom function returning parallel won't do anything

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I'm trying to implement an abstraction layer over the Gulp API by allowing easy configuration over a dedicated file.

To sum it up, I have a function (builder) that requires that file (gulpconfig.js) and calls functions that return ReadableStreams from an object the config file exports with parallel().

Here's the gist (simplified from my private source).

However, when I do gulp build, it doesn't call the TestHandler function as it should. After debugging for a while, I have identified that everything (including variable assignments etc) work perfectly fine, but it just won't execute the returned parallel() instance.

How can I fix this behaviour?

Here are the code snippets from GitHub Gist:

gulpfile.js:

/* REQUIRES */
const { parallel } = require('gulp');
const user = require('./gulpconfig');

let params = {};
let fns = [];

async function builder() {
    for (let [name, props] of Object.entries(user.config)) {
        let fnName = name;
        let fn = user[fnName];
        let src = props.src;
        let dest = props.dest;
        params[fnName] = { src, dest };
        fns.push(fn);
    }
    user.paramCp(params);
    return parallel(...fns);
}
exports.build = builder;

gulpconfig.js: 

/* REQUIRES */
const { src, dest, on, watch } = require('gulp');
const pipeline = require('readable-stream');
/* USER CONFIG */
exports.config = {
    testHandler: {
        src: "./input/*",
        dest: "./output/",
    },
};
/* LOCAL PARAM HANDLER. USED INTERNALLY. */
var params;
exports.paramCp = _params => {
    params = _params;
};
var tSrc;
var tDest;
function getParams() {
    let obj = params[getParams.caller.name];
    tSrc = obj.src;
    tDest = obj.dest;
}
/* HANDLERS. DEFINED BY handler KEY IN CONFIG */
exports.testHandler = function testHandler() {
    getParams(); // You can now use tSrc and tDest
    return pipeline(src(tSrc), dest(tDest));
};
gulp config asynchronous javascript
1 Answers

This is expected for Gulp.

gulp.parallel and gulp.series return functions (which will concurrently and serially execute their arguments, respectively). They are meant to be used in task definitions (where a function is expected) or called directly.

See this GitHub issue for more details and explanation.

Solution

Execute the function returned by parallel

    return parallel(...fns)();

Additional issue: problem with pipeline

It looks like you're trying to use pipeline here, which is not a bad idea, but your pipeline variable is not correctly defined. const pipeline = require('readable-stream'); makes pipeline of type Readable. This is the default export of the readable-stream package.

You probably want this

const { pipeline } = require('readable-stream');
user_6757210
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