@seval-ui/seval

JavaScript-like language with native TypeScript runtime

@seval-ui/seval is a JavaScript-like language with a native TypeScript runtime for evaluating logic in UI applications.

Installation

npm install @seval-ui/seval
# or
pnpm add @seval-ui/seval

Quick Start

import { compileSeval, executeSeval } from '@seval-ui/seval'

// Compile Seval code to native JavaScript object
const code = `{
  double(x) { x * 2 },
  add(a, b) { a + b }
}`

const env = compileSeval(code)

// Call methods directly on the compiled object
const result1 = env.double(5)
console.log(result1) // 10

const result2 = env.add(3, 7)
console.log(result2) // 10

// Or use executeSeval for dynamic function calls
const result3 = executeSeval(env, 'double', [5])
console.log(result3) // 10

// With state management (this-based access)
const stateCode = `{
  count: 0,
  increment() { this.count = this.count + 1 }
}`
const stateEnv = compileSeval(stateCode)

// Execute with state tracking
const state = { count: 0 }
executeSeval(stateEnv, 'increment', [], state)
console.log(state.count) // 1

Features

• Compiles to native JavaScript – Uses new Function() for zero-overhead execution
• JavaScript-like syntax – Familiar syntax with arrow functions, objects, if/else, for loops
• Line comments – Use // for single-line comments
• Lightweight – No external dependencies for runtime evaluation
• Type-safe – Full TypeScript support with type definitions
• Sandbox protection – Blocks access to dangerous reflection properties

Syntax Overview

{
  // State properties
  display: "0",
  count: 0,

  // Methods with implicit return (last expression)
  increment() {
    this.count = this.count + 1
  },

  // Single-expression functions
  double(x) { x * 2 },

  // Control flow with if/elif/else
  action(value) {
    if value > 0 {
      this.display = "positive"
    } elif value < 0 {
      this.display = "negative"
    } else {
      this.display = "zero"
    }
  },

  // For loops (three-part form)
  sum() {
    this.total = 0
    for i = 0; i < 10; i = i + 1 {
      this.total = this.total + i
    }
    this.total  // Returns 45
  },

  // For loops (condition-only form)
  countdown() {
    for this.count > 0 {
      this.count = this.count - 1
    }
  }
}

Built-in Primitives

The Seval runtime includes these built-in functions and globals:

• Arithmetic: +, -, *, /, % (+ also handles string concatenation)
• Comparison: ==, !=, ===, !==, <, <=, >, >=
• Logical: &&, ||, !
• Object helpers: merge(obj1, obj2, ...), get(obj, key)
• Globals: Math, Number, Date, String, Array, Object

Native JavaScript methods are accessible on values:

• String: s.length, s.substring(), s.includes(), s.startsWith(), s.concat()
• Array: arr.length, arr[index], arr.map(), arr.filter(), arr.concat(), arr.push()
• Object: obj.property, obj[key]

License

MIT