Opening and Saving Documents

OpenXmlSdkTs supports three I/O formats for opening and saving documents. The open() method auto-detects which format you provide, so you can use whichever is most convenient for your scenario.

Three I/O Formats

Binary Blob

The standard approach for file system I/O. Use Blob (or Buffer in Node.js) to read and write .docx, .xlsx, and .pptx files directly.

import { WmlPackage } from "openxmlsdkts";
import fs from "fs";

// Open from Blob
const buffer = fs.readFileSync("document.docx");
const doc = await WmlPackage.open(new Blob([buffer]));

// Save to Blob
const blob = await doc.saveToBlobAsync();

The type alias OpcBinary represents binary document data.

Flat OPC XML

Flat OPC is an XML representation of the entire Office document package in a single XML string. This format is especially useful for:

Office Add-ins -- The Office JavaScript API uses Flat OPC for document exchange.
XML databases -- Store documents as XML natively.
XSLT processing -- Transform documents with standard XML tools.
Debugging -- Inspect the full document structure as readable XML.

import { WmlPackage } from "openxmlsdkts";

// Open from Flat OPC string
const flatOpc: string = getFlatOpcFromSomewhere();
const doc = await WmlPackage.open(flatOpc);

// Save to Flat OPC
const flatOpcOut = await doc.saveToFlatOpcAsync();

The type alias FlatOpcString represents Flat OPC XML data.

Base64 String

A Base64-encoded representation of the binary package. Useful for:

JSON APIs -- Embed document data in JSON payloads.
Data URIs -- Use in browser contexts where data URIs are needed.
Text-based storage -- Store in systems that only support text.

import { WmlPackage } from "openxmlsdkts";

// Open from Base64 string
const base64: string = getBase64FromApi();
const doc = await WmlPackage.open(base64);

// Save to Base64
const base64Out = await doc.saveToBase64Async();

The type alias Base64String represents Base64-encoded document data.

Auto-Detection

The open() method on each package class automatically detects the input format:

// All three work with the same open() method
const doc1 = await WmlPackage.open(blob);       // Blob detected
const doc2 = await WmlPackage.open(flatOpc);     // Flat OPC XML detected
const doc3 = await WmlPackage.open(base64Str);   // Base64 detected

Format-Specific Package Classes

Use the package class that matches your document type:

Class	Document Type	Extension
`WmlPackage`	Word documents	`.docx`
`SmlPackage`	Excel workbooks	`.xlsx`
`PmlPackage`	PowerPoint presentations	`.pptx`

Save Methods

Each package provides three save methods corresponding to the three I/O formats:

Method	Returns	Description
`saveToBlobAsync()`	`Promise<Blob>`	Binary blob for file I/O
`saveToBase64Async()`	`Promise<string>`	Base64-encoded string
`saveToFlatOpcAsync()`	`Promise<string>`	Flat OPC XML string

Round-Trip Example

A typical workflow opens a document in one format, modifies it, and saves it in any format:

import { WmlPackage, W, XElement } from "openxmlsdkts";

// Open from Base64 (e.g., received from an API)
const doc = await WmlPackage.open(base64Input);

// Modify the document
const mainPart = await doc.mainDocumentPart();
const xDoc = await mainPart!.getXDocument();
const body = xDoc.root!.element(W.body);
body!.add(
  new XElement(W.p,
    new XElement(W.r,
      new XElement(W.t, "Added by OpenXmlSdkTs")
    )
  )
);
mainPart!.putXDocument(xDoc);

// Save as Flat OPC (e.g., to send to an Office Add-in)
const flatOpc = await doc.saveToFlatOpcAsync();

You can open in any format and save in any other format -- the library handles all conversions internally.