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Prepare the data

Save the following data as orders.json:

{
  "Customer": "Northwind Traders",
  "Date": "2026-09-30T00:00:00",
  "Items": [
    { "Product": "Laptop", "Quantity": 2, "Price": 1250.5 },
    { "Product": "Monitor", "Quantity": 3, "Price": 310 },
    { "Product": "Keyboard", "Quantity": 5, "Price": 45.99 }
  ]
}

Create the template

Create a Word document named invoice-template.docx with the following content. Template tags are enclosed in << and >>, and order is the name under which the data source is passed to the engine.

Invoice for <<[order.Customer]>>
Date: <<[order.Date]:"yyyy-MM-dd">>

Below the text, add a table with a header row, one data row and a total row:

Product	Quantity	Amount
`<<foreach [item in order.Items]>><<[item.Product]>>`	`<<[item.Quantity]>>`	`<<[item.Quantity * item.Price]:"0.00">><</foreach>>`
Total		`<<[order.Items.sum(i => i.Quantity * i.Price)]:"0.00">>`

The foreach tag repeats the table row for every item, and the sum extension method calculates the total. See Template Syntax for the complete syntax reference.

You can also download the ready-to-use invoice-template.docx and orders.json.

Generate the report

Create app.js next to the template and the data file:

'use strict';

const groupdocs = require('@groupdocs/groupdocs.assembly');

// Load data from the JSON file. "order" is the data source name used in the template.
const dataSource = new groupdocs.JsonDataSource("orders.json");
const dataSourceInfo = new groupdocs.DataSourceInfo(dataSource, "order");

// Build the report from the template and the data
const assembler = new groupdocs.DocumentAssembler();
assembler.assembleDocument("invoice-template.docx", "invoice.docx", dataSourceInfo);

console.log("The report is saved to invoice.docx");
process.exit(0);

Run the script:

node app.js

The generated invoice.docx contains:

Invoice for Northwind Traders
Date: 2026-09-30

Product	Quantity	Amount
Laptop	2	2501.00
Monitor	3	930.00
Keyboard	5	229.95
Total		3660.95

Note
Number and date formats follow the default locale of the Java virtual machine. Without a license, the report also contains an evaluation watermark; see Licensing and evaluation.

Save the report as PDF

To save the report in another format, pass LoadSaveOptions with the target FileFormat. This overload takes the data sources as a Java array, which you can create with the java bridge package:

'use strict';

const java = require('java');
const groupdocs = require('@groupdocs/groupdocs.assembly');

const dataSource = new groupdocs.JsonDataSource("orders.json");
const dataSourceInfo = new groupdocs.DataSourceInfo(dataSource, "order");
const dataSources = java.newArray('com.groupdocs.assembly.DataSourceInfo', [dataSourceInfo]);

// Save the report as PDF
const saveOptions = new groupdocs.LoadSaveOptions(groupdocs.FileFormat.PDF);

const assembler = new groupdocs.DocumentAssembler();
assembler.assembleDocument("invoice-template.docx", "invoice.pdf", saveOptions, dataSources);

process.exit(0);

See Changing Target File Format for more options.

Next steps

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Quick Start Guide Leave feedback

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Prepare the data

Create the template

Generate the report

Save the report as PDF

Next steps

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