Minimal gulpfile to copy Bootstrap

gulpfile-starter.js

/// <binding ProjectOpened='build' />
"use strict";

const gulp = require('gulp'),
    merge = require('merge-stream');

const roots = {
    node_modules: "./node_modules/",
    wwwroot: "./wwwroot/",
    wwwlib: "./wwwroot/lib/"
};

const paths = {
    deps: {
        "bootstrap": {
            "dist/**/*": "dist"
        },
        //"d3": {
        //    "dist/*": ""
        //},
        "jquery": {
            "dist/*": "dist"
        },
        "jquery-validation": {
            "dist/*": "dist"
        },
        "jquery-validation-unobtrusive": {
            "dist/*": ""
        },
        //"font-awesome": {
        //    "css/*": "css",
        //    "fonts/*": "fonts"
        //},
        "popper.js": {
            "dist/umd/*": ""
        }
    }
};

/**
 * Copy only the files needed by the browser for wwwroot/lib from node_modules.
 */
gulp.task("copy-lib", function () {
    var streams = [];

    // https://wildermuth.com/2017/11/19/ASP-NET-Core-2-0-and-the-End-of-Bower
    for (var prop in paths.deps) {
        for (var itemProp in paths.deps[prop]) {
            streams.push(gulp.src(roots.node_modules + prop + "/" + itemProp)
                .pipe(gulp.dest(roots.wwwlib + prop + "/" + paths.deps[prop][itemProp])));
        }
    }

    return merge(streams);
});

/**
 * Run tasks required for the build.
 */
gulp.task('build', gulp.series('copy-lib'));

/**
 * The default task invoked when gulp is run with no arguments.
 */
gulp.task('default', function (done) {
    done();
});

package.json

{
  "name": "gulpfile-starter",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "PROPRIETARY",
  "private": true,
  "devDependencies": {
    "gulp": "^4.0.2",
    "merge-stream": "^2.0.0"
  },
  "dependencies": {
    "bootstrap": "^4.4.1",
    "d3": "^5.15.0",
    "font-awesome": "^4.7.0",
    "jquery": "^3.4.1",
    "jquery-validation": "^1.19.1",
    "jquery-validation-unobtrusive": "^3.2.11",
    "popper.js": "^1.16.1"
  }
}