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Understanding JavaScript Promises: A Guide for Webflow Developers

A JavaScript Promise is an object representing the eventual completion (or failure) of an asynchronous operation. Promises are widely used in modern web development to handle tasks such as data loading and event handling, especially when integrating custom code into Webflow projects.

What is a JavaScript Promise?

  • Promise: An object that connects producing code (which might take time, like fetching data) to consuming code (which waits for the result).
  • States: A Promise can be in one of three states:
    • Pending: The operation is still ongoing.
    • Fulfilled: The operation completed successfully.
    • Rejected: The operation failed.

Basic Promise Syntax

let myPromise = new Promise(function(myResolve, myReject) {  // Producing code (may take time)  myResolve(); // if successful  myReject();  // if there’s an error});myPromise.then(  function(value) { /* code if successful */ },  function(error) { /* code if error */ });

How Promises Work

  • Producing code executes a task (like loading data).
  • When done, it calls either myResolve(result) on success or myReject(error) on failure.
  • Consuming code waits for the result using .then().
    • .then() accepts two optional callbacks: one for success, one for errors.

Example of Promise States

StatemyPromise.statemyPromise.result
Pending"pending"undefined
Fulfilled"fulfilled"result value
Rejected"rejected"error object

Note: State and result properties are internal; use methods like .then() to handle outcomes.

Simple Webflow-Relevant Example

Suppose a Webflow developer wants to load user data from an API and display it on a site once it’s available.

// Display functionfunction showUser(data) {  document.getElementById("user-info").innerHTML = data;}// Promise to fetch user datalet userPromise = new Promise(function(resolve, reject) {  fetch('https://api.example.com/user')    .then(response => {      if (response.ok) return response.json();      else reject('Error: ' + response.status);    })    .then(data => resolve('Welcome, ' + data.name + '!'))    .catch(error => reject(error));});// Consuming the PromiseuserPromise.then(  function(value) { showUser(value); },  function(error) { showUser(error); });
  • Usage: Add a <div id="user-info"></div> to the Webflow page, and this code will display a welcome message after fetching user data.

More Examples

  • Waiting for a Timeout
  let myPromise = new Promise(function(resolve, reject) {    setTimeout(function() { resolve("Action Complete!"); }, 2000);  });  myPromise.then(function(value) {    document.getElementById("demo").innerHTML = value;  });
  • Waiting for a File
  let filePromise = new Promise(function(resolve, reject) {    let req = new XMLHttpRequest();    req.open('GET', "myfile.html");    req.onload = function() {      if (req.status == 200) resolve(req.response);      else reject("File not Found");    };    req.send();  });  filePromise.then(    function(value) { /* handle file content */ },    function(error) { /* handle error */ }  );

Further Learning and Resources

Jared Malan