WXS (WeiXin Script) is a lightweight, sandboxed scripting language designed exclusively for the view layer in WeChat Mini Programs. It operates alongside WXML to enable dynamic rendering and data transformation directly within templates.

Key Characteristics

• WXS runs independently of the JavaScript execution context and cannot access global JS variables, functions, or Mini Program APIs.
• It does not rely on client-side base library versions and is compatible across all Mini Program runtime environments.
• WXS modules are isolated by design: variables and functions declared inside a module are private unless explicitly exported via module.exports.
• WXS functions cannot serve as event handlers — they are intended solely for expression evaluation and template-level logic.
• Performance varies by platform: on iOS, WXS typically executes significantly faster than JavaScript; on Android, performance is roughly equivalent.

Inline Module Declaration

WXS code can be embedded directly in WXML using the <wxs> tag:

<wxs module="formatter">
  var prefix = "WXS";
  var suffix = "Engine";
  module.exports.full = prefix + " " + suffix;
</wxs>

<view>{{formatter.full}}</view>

Output:

WXS Engine

External Module Usage

WXS logic may also reside in .wxs files. For example:

// utils.wxs
var capitalize = function(str) {
  return str.charAt(0).toUpperCase() + str.slice(1);
};

var reverse = function(arr) {
  var result = [];
  for (var i = arr.length - 1; i >= 0; i--) {
    result.push(arr[i]);
  }
  return result;
};

module.exports = {
  upper: capitalize,
  reversed: reverse
};

Referenced in WXML:

<wxs src="./utils.wxs" module="util" />
<view>{{util.upper('mini')}}</view>
<view>{{util.reversed([1, 2, 3])}}</view>

Output:

Mini
[3,2,1]

Module Resolution and Sharing

• Modules are resolved via relative paths only.
• Each .wxs file is a singleton: rpeeated imports yield the same initialized instance.
• Unreferenced modules remain unexecuted — lazy initialization applies.

Example with inter-module dependency:

// helpers.wxs
var helpers = require('./utils.wxs');

module.exports.greet = function(name) {
  return "Hello, " + helpers.upper(name) + "!";
};

<wxs src="./helpers.wxs" module="greeting" />
<view>{{greeting.greet('world')}}</view>

Output:

Hello, World!

Syntax and Scoping Rules

• Variable declarations use var, supporting hoisting.
• Undeclared assignments create implicit globals (discouraged).
• Identifiers must begin with a letter or underscore; subsequent characters may include digits.
• Reserved words (e.g., if, function, return, typeof) cannot be used as identifiers.

Valid declarations:

var _count = 0;
var isValid = true;
var user_name = "guest";

Supported Operators

Category	Examples
Arithmetic	+, -, *, /, %, **
Assignment	=, +=, <<=, &=
Comparison	<, >, <=, >=, ==, !=, ===, !==
Logical	&&, `
Bitwise	&, `
Conditional	condition ? a : b
Comma	a = 1, b = 2, a + b

String concatenation uses +, consistent with JS:

var a = "WX";
var b = "S";
console.log(a + b === "WXS"); // true

Control Flow Statements

Conditional Logic

if (score >= 90) {
  grade = "A";
} else if (score >= 80) {
  grade = "B";
} else {
  grade = "C";
}

Switch Statement

Only literal values (string, number) and identifier references are allowed in case clauses:

switch (status) {
  case "active":
    stateCode = 200;
    break;
  case 1:
    stateCode = 400;
    break;
  default:
    stateCode = 500;
}

Loops

Both for and while loops support break and continue:

var sum = 0;
for (var i = 0; i < 5; i++) {
  if (i === 3) break;
  sum += i;
}
// sum === 6

Data Types

WXS supports seven primitive and composite types:

• number: integers and floats (42, 3.14)
• string: quoted literals ('text', "data")
• boolean: true, false
• object: key-value collections ({ a: 1, b: 'x' })
• array: ordered lists ([1, 'two', {}])
• function: callable entities (function(x) { return x * 2; })
• date: time instances created via getDate()
• regexp: pattern objects via getRegExp(pattern, flags)

Type introspection is possible through constructor or typeof:

var now = getDate();
console.log(now.constructor === "Date"); // true
console.log(typeof now); // "object"

var nums = [1, 2];
console.log(nums.constructor === "Array"); // true
console.log(typeof nums); // "object"

Built-in Objects

console

Provides log() for debugging output in developer tools.

Math

Standard mathematical constants and functions:

var maxVal = Math.max(5, 12, 3); // 12
var rand = Math.random(); // 0–1 float

JSON

Supports serialization and parsing:

var obj = { id: 1, name: "test" };
var jsonStr = JSON.stringify(obj); // "{\"id\":1,\"name\":\"test\"}"
var parsed = JSON.parse(jsonStr); // { id: 1, name: "test" }

Number, Date, Global

Expose standard static properties (Number.MAX_VALUE, Date.now(), isNaN(), etc.) following ES5 semantics.

Module Export Patterns

Exports may be assigned via object literal or direct property assignment:

// style A
module.exports = {
  format: function(s) { return s.trim().toUpperCase(); },
  PI: 3.14159
};

// style B
var helper = function(x) { return x + 1; };
module.exports.inc = helper;
module.exports.version = "1.0";

Imported modules expose these exports under the declared module name in WXML.