Technical Forecast: ECMAScript 2025 Finalized Feature Analysis: Make JavaScript More Elegant

As one of the most widely used programming languages ​​in the world, JavaScript continues to evolve through the ECMAScript standard every year. In 2025, ECMAScript once again brought a number of major updates, and this article will take you to explain in depthThe core features that have been officially finalized，

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1. Smarter asynchronous processing:

Problem background: Problem of the problem of synchronous functions and asynchronous Promise exception handling code separation

// Traditional methods require manual wrapping of synchronization functions
 function fetchData() {
   if (() < 0.5) throw new Error('Synchronous Error');
   return ('data');
 }

 // ES2025 new solution
 (fetchData)
   .then(data => (data))
   .catch(err => ('Unified capture:', err));
  
 //Traditional plan
 try{
 fetchData
   .then(data => (data))
   .catch(err => ('Unified capture:', err));
 } catch{

 }

Advantages：

• 1. Synchronization errors automatically convert to Promise rejection
• 2. Avoid nested statements, unified asynchronous code and synchronous code exception handling
• 3. Execution timing is more intuitive (synchronous function is executed immediately)

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2. Set operation: Set method enhancement

Added API：

const devs = new Set(['Alice', 'Bob']);
 const seniors = new Set(['Alice', 'Charlie']);

 // Intersection: Have both development and senior identities
 (seniors); // Set {'Alice'}

 //Difference: Ordinary developers
 (seniors); // Set {'Bob'}

 // Union: All relevant personnel
 (seniors); // Set {'Alice','Bob','Charlie'}

This new API reminds me of Python's intersection union operation

With the rapid development of Javascript, it has now become the language with the most flexible and fastest syntax, and more and more Python's syntax features have been borrowed by Javascript.

Life is short, I use pythonThe protagonist of this sentence may be replaced by Javascript

So leave a question of thinking. Will Python eventually be replaced by more flexible JS?

3. Regular expressions:

1. Repeat the name of the capture group

In traditional regular expressions, if multiple branches need to capture the same type of data but the format is different, the developer must define a different group name for each branch:

// Old solution: Different formats require different group names
 const OLD_DATE_REGEX = /^
   (?<y>\d{4})-(?<m>\d{2})-(?<d>\d{2}) // Format 1: YYYY-MM-DD
   |
   (?<m2>\d{2})\/(?<d2>\d{2})\/(?<y2>\d{4}) // Format 2: MM/DD/YYYY
 $/;

 // You need to manually determine the matching branch
 const { y, m, d } = || {};
 const year = y || .y2; // Redundant conditional judgment

Advantages of new grammars
After capturing groups with duplicate naming, different branches can reuse the same group name and directly access the data through the unified field:

// ES2025 new plan: Unified group names
 const DATE_REGEX = /^
   (?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})
   |
   (?<month>\d{2})\/(?<day>\d{2})\/(?<year>\d{4})
 $/;

 // Direct deconstruction without conditional judgment
 const { year, month, day } = ; // Automatically match the group of the corresponding branch

2. Regular expression local modifier

Precise control matching rules:

// Enable Ignore case only for some modes
 const re = /HELLO(?i: World)/;
 ('HELLO world'); // true (World part is case-insensitive)

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4. Other important updates

Deferred Module Evaluation
Optimize startup performance of large applications:

// Load heavy modules on demand
 defer import heavyModule from './';
  = async() => {
   await (); // Load when clicked
 };

So I have a question here? Are they all loaded on demand? What is the essential difference between this and dynamic loading scheme?

Technical details comparison

1. Delay module loading

• Preload: The module starts loading at declaration (parallel to the main thread), butNo module code execution。
• Delayed execution: Execution of module code is delayed until the first time it accesses its export member.

Example：

// Preload the module when declared (no code execution)
 defer import { heavyModule } from './';

  = async() => {
   // The module is triggered to execute when clicked (the module has been loaded at this time)
   await ();
 };

Advantages：

• Reduces CPU usage during initialization (module code delays execution).
• Resource preload optimization avoids waiting for network requests during runtime.

2. Dynamic import(ES6 features)

• Load on demand: Calledimport()triggers asynchronous loading of modules andExecute now。
• Promise Driver: Return to Promise, need to passawaitor.then()deal with.

Example：

// Trigger loading and execution when clicked
  = async() => {
   const { heavyModule } = await import('./');
   ();
 };

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Use scenarios

Scenario 1: Use delay module loading to solveHome screen optimizationThe problem

Although we can use it nowLazy loadingorLoad on demandThe method to optimize the first screen,

However, both solutions have a common pain point, which is the extremely poor user experience (users cannot see the content in real time, and sometimes we need to use hack techniques to preload these modules that need to be loaded on demand)

Lazy loading scheme problem:
Lazy loading scheme will cause the user to drag to the viewport of the hidden area before it will trigger loading. If it is an area dominated by the image, the user will see a period of white screen time. Generally, we will solve it by combining preloading.

Dynamic import issues:
Dynamic introduction solutions, especially pop-up resources, will cause white screens and splash screens when you first open them.

Delay module loading is inherently equipped with preload and on-demand loading, so it greatly simplifies our code.

• Dynamic import: Suitable for secondary features that fully load on demand (such as settings pages).

Scenario 2: Complex dependency management

// Delayed module loading: dependency is preloaded but not executed
 defer import { A } from './';
 defer import { B } from './';

 async function run() {
   // Code that triggers A and B during execution
   await ();
   await ();
 }

 // Dynamic import: Runtime load dependencies on demand
 async function loadDependencies() {
   const { A } = await import('./');
   const { B } = await import('./');
   await ();
   await ();
 }

Scenario 3: Performance-sensitive applications

• Delay module loading: Suitable for scenarios that require rapid response to user interaction (such as media resources, pop-up resources, and preloading of large module resources).
• Dynamic import: Suitable for any on-demand loading scenario, such as routing page switching

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4. Differences in underlying mechanisms

stage	Delay module loading	Dynamic import
load	Trigger loading when declared (in parallel with HTML parsing)	Trigger loading when called
Analysis/Compilation	Complete immediately after loading	Complete immediately after loading
implement	Delayed until the first access to export	Execute immediately after loading
cache	Global module cache (shared with static import)	Global module cache (shared with static import)

characteristic	Delay module loading (Deferred Import)	Dynamic import (Dynamic Import)
grammar	defer import { ... } from '...'	await import('...')
Loading time	Preloaded when declared, trigger execution when accessed	Load and execute asynchronously when called
Execution order	Module code is delayed until first access	Execute the module code immediately
Whether to block the main thread	Non-blocking (preloading resources, delayed execution)	Non-blocking (asynchronous loading)
Applicable scenarios	Modules that require preload but delay execution	Code segmentation scenarios that are loaded on demand

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Summarize

• Delay module loading = Preload + Delayed execution→ Optimize initialization performance
• Dynamic import = Load on demand + Instant execution→ Implement code segmentation

The two can be used in combination:defer importPreload key modules withimport()Process dynamic routing to achieve optimal performance balance.