gulpfile.js

const gulp = require("gulp");
const ts = require("gulp-typescript");

let tsProject = ts.createProject("tsconfig.json");

gulp.task("scripts", () => {
    const tsResult = tsProject.src()
        .pipe(tsProject());
    return tsResult.js.pipe(gulp.dest('dist'));
});

gulp.task("watch", ['scripts'], () => {
    gulp.watch('src/**/*.ts', ['scripts']);
});

gulp.task('default', ['watch']);