Convert demo to Gulp 4.0.0+

[13rac1]

Conversion of the Gulp demo/example code from API 3 to 4.

• HighlightJS automatically and manually applied.
• Switched from var to const for require() calls.

[attaradev]

Great, I was about to do the same and saw this PR. Kindly merge it to reflect the current state of gulp. Because the current demo is breaking and frustrating a lot of developers thereby affecting the developer experience.

[yocontra]

This can be simplified a lot IMO - the demo is supposed to be as simple and readable as possible.

• Destructuring is a bit of a stretch here, would prefer just accessing off gulp
• Arrow functions on the tasks would be nice
• Export each task function

[phated]

I'm going to clean this up and get it released today

[13rac1]

the demo is supposed to be as simple and readable as possible.

@contra I agree, but wanted to open this PR with the minimal line count changes. I'd have been happy to refactor further pre-merge. @phated merging works though!

Destructuring is a bit of a stretch here, would prefer just accessing off gulp
Arrow functions on the tasks would be nice
Export each task function

I thought it strange too. That is what the documentation shows, so I matched it. The docs should be updated for consistency if this example is changed to use arrow functions or direct gulp access.

Example:

const { src, dest } = require('gulp');

function streamTask() {
  return src('*.js')
    .pipe(dest('output'));
}

From https://gulpjs.com/docs/en/getting-started/async-completion#returning-a-stream and copied for posterity in case of change.

[phated]

As per the documentation rewrite:

• Named functions are preferred over arrow functions
• Destructuring is preferred over using gulp namespace

Those changes have stayed in my merge but I cleaned up how they are displayed on desktop and mobile.