How Uni API Enables True Write‑Once‑Run‑Everywhere for Mini‑Programs

With major mobile app vendors releasing their own mini‑program solutions, developers face the challenge of supporting multiple platforms with a single codebase. Existing cross‑platform frameworks (Rax, uniapp, Taro, Remax) address UI reuse, but the API layer lacks a standard, leading to duplicated and complex code.

After experiences with community group‑buying mini‑programs, Alibaba's digital agriculture team created Uni API to bridge API differences between mini‑program containers and the web, providing a solid foundation for "write once, run everywhere".

What is Uni API?

Supports Web, WeChat Mini‑Program, ByteDance Mini‑Program, Alipay Mini‑Program, Baidu Mini‑Program, Kuaishou Mini‑Program

No framework dependency

Bilingual documentation and rich examples

Implements 101 common APIs, with on‑demand loading and unused‑code removal

Comprehensive TypeScript declarations for better IDE support

Problems Uni API Solves

Inconsistent API prefixes (e.g., tt., wx.) across containers

Different input/output parameter specifications

Lack of TypeScript declarations in native APIs

Need to consult multiple platform docs and write compatibility code, inflating bundle size

Missing web implementations hinder debugging

Specification

Based on the WeChat Mini‑Program API spec, Uni API defines a unified set of 101 APIs and classifies them into four categories:

APIs identical across containers (same parameters and behavior)

APIs with differences that can be abstracted away

APIs with differences that cannot be unified

Container‑specific APIs not supported in the common set

For the first two categories, Uni API removes prefixes or normalizes parameters; for the third, it exposes the subset of capabilities while preserving differences; the fourth category is not included.

Input Normalization

Parameters are unified, and platform‑specific differences are handled via an _ext field. Example:

import showActionSheet from '@uni/action-sheet';
showActionSheet({
  itemList: ['A', 'B', 'C'],
  _ext: {
    aliMiniApp: { title: 'Extra title for Alipay' },
    wechatMiniProgram: { itemColor: '#ff1214' }
  }
}).then(res => {
  console.log(`Selected index: ${res.tapIndex}`);
});

Only the relevant fields are applied in each container.

Output Normalization

Uni API standardizes return values, flattening differences while preserving any extra fields for developers to use.

Core Capabilities

True cross‑platform support that abstracts environment differences

Framework‑agnostic usage in native mini‑program projects or any cross‑platform framework

Promise‑based asynchronous APIs for easier maintenance

Full TypeScript declarations for IDE auto‑completion and error checking

Unified error handling

Extensive API coverage (100+ APIs, 70+ in the first release) with minimal bundle size

Supporting Features

Bilingual documentation covering every API and parameter

Real‑device demos for all supported platforms

CanIUse tool to detect API support at runtime

How to Use Uni API

Install either a small package for a single API or the full package for all APIs:

npm install --save @uni/storage
import { getStorageSync } from '@uni/storage';
getStorageSync({ key: 'key' });

npm install --save @uni/apis
import { confirm, storage } from '@uni/apis';
confirm({ content: 'Show modal' });
storage.getStorageSync({ key: 'key' });

Use Babel or Rax plugins to tree‑shake unused code and achieve the smallest possible bundle.

Design Approach

Uni API is built atomically: each API is a module independent of container, resulting in 65 APIs across six containers (390 implementations) today, and a planned 101 APIs across six containers (606 modules) in the future.

Conclusion

Uni API addresses the misalignment of mini‑program and web APIs, offering a lightweight, cross‑platform solution that lets developers focus on business logic rather than compatibility, moving closer to a perfect write‑once‑run‑everywhere experience.

Related links: Uni API website , Rax website , GitHub repository , Issue tracker .