CSOM, JSOM and REST API in SharePoint : Quick Overview

When developing solutions for SharePoint, one of the most common questions that arises is: “Should I use CSOM, JSOM, or the REST API?” These three client-side development models serve similar purposes—interacting with SharePoint data remotely—but each comes with its own strengths, quirks, and ideal use cases. Whether you’re building a web part, automating tasks, or integrating external apps, knowing when and how to use these APIs can make all the difference in your SharePoint journey.

In this blog, we’ll break down what CSOM, JSOM, and REST API are, why we need them, who typically uses them, best practices, real-life implementation scenarios, and how they compare with one another.

What Are CSOM, JSOM, and REST API?

CSOM (Client-Side Object Model)
CSOM is a .NET-based API that allows developers to interact with SharePoint data from client applications like console apps, Windows apps, and PowerShell scripts. It’s commonly used in SharePoint Add-ins, Office 365 automation scripts, and migration tools. Microsoft provides CSOM libraries for .NET and Silverlight.
JSOM (JavaScript Object Model)
JSOM is essentially the JavaScript equivalent of CSOM. It allows developers to interact with SharePoint from within the browser, making it ideal for custom scripts, UI interactions, and content manipulation on modern pages and classic web parts. JSOM is widely used in Script Editor Web Parts and older SharePoint solutions.
REST API (Representational State Transfer)
The REST API is a powerful web service interface that allows applications to interact with SharePoint over HTTP. It’s lightweight, flexible, and accessible from almost any language that can make HTTP requests, making it popular among frontend developers, mobile apps, and third-party integration systems.

Why Do We Need These APIs?

These APIs are the backbone of client-side development in SharePoint. They enable us to:

Create, read, update, and delete SharePoint data
Automate administrative tasks and data manipulation
Build scalable apps that interact with SharePoint content
Integrate external services and applications
Create rich user experiences and custom UIs
Replace server-side code in cloud-friendly, sandboxed solutions

In the modern SharePoint ecosystem, client-side development is more than just a trend—it’s the preferred and often only approach, especially in SharePoint Online where full-trust server-side code is not allowed.

Who Uses It and Where Is It Used?

CSOM is primarily used by back-end developers, system administrators, and DevOps engineers working on automation scripts, migrations, provisioning solutions, and legacy integrations.
JSOM is used by front-end developers, business users, and consultants who need to build UI enhancements within classic SharePoint pages.
REST API is favored by full-stack developers, Power Platform builders, and modern web developers looking to integrate SharePoint with other systems or build SPFx (SharePoint Framework) solutions.

These APIs are commonly used in:

PowerShell scripts
Office Add-ins
SPFx Web Parts
Power Automate custom connectors
Intranet portals
Third-party dashboards and mobile apps

Sample Code Snippets

🧑‍💻 CSOM (C#):

using Microsoft.SharePoint.Client;

ClientContext context = new ClientContext("https://contoso.sharepoint.com/sites/demo");
List list = context.Web.Lists.GetByTitle("Documents");
context.Load(list);
context.ExecuteQuery();

Console.WriteLine("List Title: " + list.Title);

🌐 JSOM (JavaScript):

var ctx = SP.ClientContext.get_current();
var list = ctx.get_web().get_lists().getByTitle("Documents");
ctx.load(list);

ctx.executeQueryAsync(function () {
    console.log("List Title: " + list.get_title());
}, function (sender, args) {
    console.error('Error: ' + args.get_message());
});

🔗 REST API (JavaScript with Fetch):

fetch("https://contoso.sharepoint.com/sites/demo/_api/web/lists/getbytitle('Documents')", {
    method: "GET",
    headers: {
        "Accept": "application/json;odata=verbose"
    }
})
.then(response => response.json())
.then(data => console.log("List Title: " + data.d.Title))
.catch(error => console.error("Error:", error));

Pros and Cons

Feature	CSOM	JSOM	REST API
Language	C# / .NET	JavaScript	Any (HTTP)
Ease of Use	Strong for .NET devs	Native for browser	Flexible, stateless
Modern Compatibility	✅	🚫 (less used now)	✅
Performance	Medium	Medium	High (stateless)
Documentation	Extensive	Moderate	Excellent
Batch Support	✅	✅	✅ (via `$batch`)
Cross-platform	🚫 (Windows-heavy)	✅	✅
Error Handling	Structured	Callback-heavy	Flexible (try/catch)

Best Practices

Choose REST API for modern solutions, especially in SPFx or integration scenarios.
Use CSOM when working with complex administrative or provisioning tasks in .NET or PowerShell.
Avoid JSOM in new development unless you are enhancing a legacy system.
Optimize queries by loading only the fields you need (especially in CSOM and JSOM).
Batch your requests to reduce round-trips and latency.
Always handle errors gracefully with try/catch (or executeQueryAsync failure callbacks).
Leverage $select and $expand in REST API to reduce payloads and include relational data.

Use Cases and Sample Implementations

CSOM Use Case: A migration tool moving documents from SharePoint 2013 to SharePoint Online with metadata.
JSOM Use Case: A Script Editor Web Part that dynamically filters list items based on user input.
REST API Use Case: A React-based SPFx web part that retrieves tasks from a SharePoint list and visualizes them in a calendar.

Comparison: REST API vs Graph API

While REST is native to SharePoint, Microsoft Graph API is an alternative that allows you to interact with broader Microsoft 365 data, including SharePoint, OneDrive, Teams, and Outlook.

Feature	REST API	Graph API
Scope	SharePoint-specific	Cross-platform (Teams, Outlook, etc.)
Endpoint	`_api/web/lists`	`graph.microsoft.com/v1.0/sites`
Token	SharePoint token	Azure AD token
Flexibility	High	Very high
Use Case	SharePoint CRUD operations	Enterprise integrations

For instance, to get a list from SharePoint:

REST API:
https://contoso.sharepoint.com/sites/demo/_api/web/lists/getbytitle('Tasks')
Graph API:
https://graph.microsoft.com/v1.0/sites/contoso.sharepoint.com:/sites/demo:/lists/Tasks

When it comes to SharePoint development, understanding the differences between CSOM, JSOM, and REST API is essential. These tools provide the flexibility and functionality required to build scalable, cloud-friendly, and user-friendly solutions.

Use CSOM for backend automation and admin tasks.
Use JSOM for legacy SharePoint pages, if needed.
Use REST API for modern solutions, SPFx, and integrations.

If you’re starting a new project in SharePoint Online, REST is almost always your best bet due to its versatility and alignment with Microsoft’s cloud-first strategy.