JSFiddle - React, Tailwind, and code Playground

JavaScript

var len = Array.from({length:100000})
    
    // named function
    function _named() {

        console.profile("named function");
        console.time("named function");

        function resolver(resolve, reject) {
          resolve("named function")
        }

        function done(data) {
          console.log(data)
        }

        function complete() {
          console.timeEnd("named function");
          console.profileEnd();
          return "named function complete"
        }

        function callback() {
          return new Promise(resolver).then(done)
        }

        return Promise.all(len.map(callback)).then(complete);
      }

    // anonymous function
    function _anonymous() {
        console.profile("anonymous function");
        console.time("anonymous function");

        return Promise.all(len.map(function() {
            return new Promise(function(resolve, reject) {
                resolve("anonymous function")
              })
              .then(function(data) {
                console.log(data)
              })
          }))
          .then(function() {
            console.timeEnd("anonymous function");
            console.profileEnd();
            return "anonymous function complete"
          })
      }
      
    // arrow function
    function _arrow() {
      console.profile("arrow function");
      console.time("arrow function");

      return Promise.all(len.map(() => {
          return new Promise((resolve, reject) =>
              resolve("arrow function")
            )
            .then((data) => {
              console.log(data)
            })
        }))
        .then(() => {
          console.timeEnd("arrow function");
          console.profileEnd();
          return "arrow function complete"
        })
    }

    _named().then(_anonymous).then(_arrow)