xlsx-handlebars 0.1.3

A Rust library for processing XLSX files with Handlebars templates, supporting WASM, Node.js, Deno, and browsers
Documentation

xlsx-handlebars

Crates.io Documentation License

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A Rust library for processing XLSX files with Handlebars templates, supporting multiple platforms:

  • 🦀 Rust Native
  • 🌐 WebAssembly (WASM)
  • 📦 npm Package
  • 🟢 Node.js
  • 🦕 Deno
  • 🌍 Browser
  • 📋 JSR (JavaScript Registry)

Features

  • ✅ Smart Merge: Automatically handles Handlebars syntax split by XML tags
  • ✅ XLSX Validation: Built-in file format validation to ensure valid input files
  • ✅ Handlebars Support: Full template engine with variables, conditions, loops, and Helper functions
  • ✅ Cross-Platform: Rust native + WASM support for multiple runtimes
  • ✅ TypeScript: Complete type definitions and IntelliSense
  • ✅ Zero Dependencies: WASM binary with no external dependencies
  • ✅ Error Handling: Detailed error messages and type-safe error handling

Installation

Rust

cargo add xlsx-handlebars

npm

npm install xlsx-handlebars

Deno

import { render, init } from "jsr:@sail/xlsx-handlebars";

Usage Examples

Rust

use xlsx_handlebars::render_handlebars;
use serde_json::json;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Read XLSX template file
    let template_bytes = std::fs::read("template.xlsx")?;
    
    // Prepare data
    let data = json!({
        "name": "John Doe",
        "company": "ABC Tech Inc.",
        "position": "Software Engineer",
        "projects": [
            {"name": "Project A", "status": "Completed"},
            {"name": "Project B", "status": "In Progress"}
        ],
        "has_bonus": true,
        "bonus_amount": 5000
    });
    
    // Render template
    let result = render_handlebars(template_bytes, &data)?;
    
    // Save result
    std::fs::write("output.xlsx", result)?;
    
    Ok(())
}

JavaScript/TypeScript (Node.js)

import { render, init } from 'xlsx-handlebars';
import fs from 'fs';

async function processTemplate() {
    // Initialize WASM module
    await init();
    
    // Read template file
    const templateBytes = fs.readFileSync('template.xlsx');
    
    // Prepare data
    const data = {
        name: "Jane Smith",
        company: "XYZ Technology Ltd.",
        position: "Senior Developer",
        projects: [
            { name: "E-commerce Platform", status: "Completed" },
            { name: "Mobile App", status: "In Development" }
        ],
        has_bonus: true,
        bonus_amount: 8000
    };
    
    // Render template
    const result = render(templateBytes, JSON.stringify(data));
    
    // Save result
    fs.writeFileSync('output.xlsx', new Uint8Array(result));
}

processTemplate().catch(console.error);

Deno

import { render, init } from "https://deno.land/x/xlsx_handlebars/mod.ts";

async function processTemplate() {
    // Initialize WASM module
    await init();
    
    // Read template file
    const templateBytes = await Deno.readFile("template.xlsx");
    
    // Prepare data
    const data = {
        name: "Alice Johnson",
        department: "R&D",
        projects: [
            { name: "AI Customer Service", status: "Live" },
            { name: "Data Visualization Platform", status: "In Development" }
        ]
    };
    
    // Render template
    const result = render(templateBytes, JSON.stringify(data));
    
    // Save result
    await Deno.writeFile("output.xlsx", new Uint8Array(result));
}

if (import.meta.main) {
    await processTemplate();
}

Browser

<!DOCTYPE html>
<html>
<head>
    <title>XLSX Handlebars Example</title>
</head>
<body>
    <input type="file" id="fileInput" accept=".xlsx">
    <button onclick="processFile()">Process Template</button>
    
    <script type="module">
        import { render, init } from './pkg/xlsx_handlebars.js';
        
        // Initialize WASM
        await init();
        
        window.processFile = async function() {
            const fileInput = document.getElementById('fileInput');
            const file = fileInput.files[0];
            
            if (!file) return;
            
            const arrayBuffer = await file.arrayBuffer();
            const templateBytes = new Uint8Array(arrayBuffer);
            
            const data = {
                name: "John Doe",
                company: "Example Company"
            };
            
            try {
                const result = render(templateBytes, JSON.stringify(data));
                
                // Download result
                const blob = new Blob([new Uint8Array(result)], {
                    type: 'application/vnd.openxmlformats-officedocument.wordprocessingml.document'
                });
                const url = URL.createObjectURL(blob);
                const a = document.createElement('a');
                a.href = url;
                a.download = 'processed.xlsx';
                a.click();
            } catch (error) {
                console.error('Processing failed:', error);
            }
        };
    </script>
</body>
</html>

Template Syntax

Basic Variable Substitution

Employee Name: {{name}}
Company: {{company}}
Position: {{position}}

Conditional Rendering

{{#if has_bonus}}
Bonus: ${{bonus_amount}}
{{else}}
No Bonus
{{/if}}

{{#unless is_intern}}
Full-time Employee
{{/unless}}

Loop Rendering

Project Experience:
{{#each projects}}
- {{name}}: {{description}} ({{status}})
{{/each}}

Skills:
{{#each skills}}
{{@index}}. {{this}}
{{/each}}

Helper Functions

Built-in Helper functions:

<!-- Basic helpers -->
{{upper name}}           <!-- Convert to uppercase -->
{{lower company}}        <!-- Convert to lowercase -->
{{len projects}}         <!-- Array length -->
{{#if (eq status "completed")}}Completed{{/if}}    <!-- Equality comparison -->
{{#if (gt score 90)}}Excellent{{/if}}              <!-- Greater than comparison -->
{{#if (lt age 30)}}Young{{/if}}                    <!-- Less than comparison -->

<!-- String concatenation -->
{{concat "Hello" " " "World"}}                     <!-- String concatenation -->
{{concat "Total: " count}}                         <!-- Mix strings and variables -->

<!-- Excel-specific helpers -->
{{num employee.salary}}                            <!-- Mark cell as number type -->
{{formula "=SUM(A1:B1)"}}                         <!-- Static Excel formula -->
{{formula (concat "=SUM(" (_c) "1:" (_c) "10)")}} <!-- Dynamic formula with current column -->
{{mergeCell "C4:D5"}}                             <!-- Merge cells C4 to D5 -->
{{img logo.data 100 100}}                          <!-- Insert image with width and height -->

<!-- Column name conversion helpers -->
{{toColumnName "A" 5}}                             <!-- A + 5 offset = F -->
{{toColumnName (_c) 3}}                            <!-- Current column + 3 offset -->
{{toColumnIndex "AA"}}                             <!-- AA column index = 27 -->

Excel Formula Helpers

Static Formula:

<!-- In Excel cell -->
{{formula "=SUM(A1:B1)"}}
{{formula "=AVERAGE(C2:C10)"}}
{{formula "=IF(D1>100,\"High\",\"Low\")"}}

Dynamic Formula with concat:

<!-- Dynamic row reference -->
{{formula (concat "=A" (_r) "*B" (_r))}}

<!-- Dynamic column reference -->
{{formula (concat "=SUM(" (_c) "2:" (_c) "10)")}}

<!-- Complex dynamic formula -->
{{formula (concat "=IF(" (_cr) ">100,\"High\",\"Low\")")}}

Available position helpers:

  • (_c) - Current column letter (A, B, C, ...)
  • (_r) - Current row number (1, 2, 3, ...)
  • (_cr) - Current cell reference (A1, B2, C3, ...)

Column Name Conversion Helpers

toColumnName - Convert column name or index to a new column name with optional offset:

<!-- Basic usage: offset from specified column -->
{{toColumnName "A" 0}}     <!-- A (no offset) -->
{{toColumnName "A" 5}}     <!-- F (A + 5) -->
{{toColumnName "Z" 1}}     <!-- AA (Z + 1) -->

<!-- Use with current column -->
{{toColumnName (_c) 3}}    <!-- Current column + 3 offset -->

<!-- Application in dynamic formulas -->
{{formula (concat "=SUM(" (_c) "1:" (toColumnName (_c) 3) "1)")}}
<!-- Example: If current column is B, generates formula =SUM(B1:E1) -->

toColumnIndex - Convert column name to column index (1-based):

{{toColumnIndex "A"}}      <!-- 1 -->
{{toColumnIndex "Z"}}      <!-- 26 -->
{{toColumnIndex "AA"}}     <!-- 27 -->
{{toColumnIndex "AB"}}     <!-- 28 -->

Merge Cells Helper

mergeCell - Mark cell ranges that need to be merged:

<!-- Static cell merging -->
{{mergeCell "C4:D5"}}      <!-- Merge C4 to D5 region -->
{{mergeCell "F4:G4"}}      <!-- Merge F4 to G4 region -->

<!-- Dynamic cell merging: from current position -->
{{mergeCell (concat (_c) (_r) ":" (toColumnName (_c) 3) (_r))}}
<!-- Example: If current is B5, merges B5:E5 (4 columns to the right) -->

<!-- Dynamic cell merging: spanning rows and columns -->
{{mergeCell (concat (_c) (_r) ":" (toColumnName (_c) 2) (add (_r) 2))}}
<!-- Example: If current is C3, merges C3:E5 (3×3 region) -->

<!-- Dynamic merging in loops -->
{{#each sections}}
  {{mergeCell (concat "A" (add @index 2) ":D" (add @index 2))}}
  <!-- Merge columns A-D for each section row -->
{{/each}}

Notes:

  • mergeCell produces no output, only collects merge information
  • Merge range format must be StartCell:EndCell (e.g., "A1:B2")
  • Duplicate merge ranges are automatically deduplicated
  • Merge information is automatically added to the Excel file after rendering

Number Type Helper

Use {{num value}} to ensure a cell is treated as a number in Excel:

<!-- Without num: treated as text -->
{{employee.salary}}

<!-- With num: treated as number -->
{{num employee.salary}}

This is especially useful when:

  • The value might be a string but should be treated as a number
  • You want to ensure proper number formatting in Excel
  • You need the value to work in formulas

Image Insertion Helper

img - Insert base64-encoded images into Excel:

<!-- Basic usage: insert image with original dimensions -->
{{img logo.data}}

<!-- Specify width and height (in pixels) -->
{{img photo.data 150 200}}

<!-- Use dimensions from data -->
{{img image.data image.width image.height}}

Features:

  • ✅ Supports common image formats: PNG, JPEG, WebP, BMP, TIFF, GIF
  • ✅ Auto-detects actual image dimensions
  • ✅ Optional width and height specification (in pixels)
  • ✅ Image positioned at current cell location
  • ✅ Images are not constrained by cell size, maintain aspect ratio
  • ✅ Supports multiple images in the same sheet
  • ✅ Supports images in multiple sheets
  • ✅ Uses UUID to avoid ID conflicts

Complete Example:

// Prepare image data in JavaScript
import fs from 'fs';

const imageBuffer = fs.readFileSync('logo.png');
const base64Image = imageBuffer.toString('base64');

const data = {
  company: {
    logo: base64Image,
    name: "Tech Company"
  },
  products: [
    {
      name: "Product A",
      photo: base64Image,
      width: 120,
      height: 120
    },
    {
      name: "Product B", 
      photo: base64Image,
      width: 100,
      height: 100
    }
  ]
};

// Use in template

<!-- Excel template example -->
Company Logo: {{img company.logo 100 50}}

Product List:
{{#each products}}
Product Name: {{name}}
Image: {{img photo width height}}
{{/each}}

Usage Tips:

  • If only width is specified, height scales proportionally
  • If only height is specified, width scales proportionally
  • If neither is specified, original image dimensions are used
  • Image will be placed at the cell location where {{img}} is called
  • base64 data should not include the data:image/png;base64, prefix, just the pure base64 string

Complex Example

=== Employee Report ===

Basic Information:
Name: {{employee.name}}
Department: {{employee.department}}
Position: {{employee.position}}
Hire Date: {{employee.hire_date}}

{{#if employee.has_bonus}}
💰 Bonus: ${{employee.bonus_amount}}
{{/if}}

Project Experience (Total {{len projects}}):
{{#each projects}}
{{@index}}. {{name}}
   Description: {{description}}
   Status: {{status}}
   Team Size: {{team_size}} people
   
{{/each}}

Skills Assessment:
{{#each skills}}
- {{name}}: {{level}}/10 ({{years}} years of experience)
{{/each}}

To remove an entire row in a table, simply add to any cell:
{{removeRow}}


{{#if (gt performance.score 90)}}
🎉 Performance Rating: Excellent
{{else if (gt performance.score 80)}}
👍 Performance Rating: Good
{{else}}
📈 Performance Rating: Needs Improvement
{{/if}}

Error Handling

The library provides detailed error types and messages:

Rust

use xlsx_handlebars::{render_handlebars, XlsxError};

match render_handlebars(template_bytes, &data) {
    Ok(result) => {
        println!("Processing successful!");
        std::fs::write("output.xlsx", result)?;
    }
    Err(e) => match e.downcast_ref::<XlsxError>() {
        Some(XlsxError::InvalidZipFormat) => {
            eprintln!("Error: Invalid XLSX file format");
        }
        _ => {
            eprintln!("Other error: {}", e);
        }
    }
}

JavaScript/TypeScript

try {
    const result = render(templateBytes, JSON.stringify(data));
    console.log('Processing successful!');
} catch (error) {
    console.error('Processing failed:', error);
}

Build and Development

Build WASM Package

# Build all targets
npm run build

# Or build separately
npm run build:web    # Browser version
npm run build:npm    # Node.js version 
npm run build:jsr    # Deno version

Run Examples

# Rust example
cargo run --example rust_example

# Node.js example
node examples/node_example.js

# Deno example  
deno run --allow-read --allow-write examples/deno_example.ts

# Browser example
cd tests/npm_test
node serve.js
# Then open http://localhost:8080 in your browser
# Select examples/template.xlsx file to test

Technical Features

Smart Merge Algorithm

The core innovation of this library is the smart merge of Handlebars syntax split by XML tags. In XLSX files, when users input template syntax, Excel may split it into multiple XML tags.

Performance and Compatibility

  • Zero-Copy: Efficient memory management between Rust and WASM
  • Streaming: Suitable for processing large XLSX files
  • Cross-Platform: Supports Windows, macOS, Linux, Web
  • Modern Browsers: Supports all modern browsers with WASM support

License

This project is licensed under the MIT License - see the LICENSE-MIT file for details.

Support

Support this project with a donation via Alipay:

Support this project with a donation