Get Custom Master Page Url of a SharePoint Site using REST API

This blog contains the syntax and code snippet to get the custom master page url from the SharePoint site using REST API.

Syntax

REST API Endpoint:

https://SharePointSiteURL/_api/web?$select=CustomMasterUrl

REST API endpoint to use in Add-ins:

<appweburl>/_api/SP.AppContextSite(@target)/web?$select=CustomMasterUrl&@target=<hostweburl>

Embed Code Snippet

The following code snippet can be added to SharePoint page or in content editor web part as a script. This example is used to get the custom master page URL of a SharePoint site and this returns the site relative url.

<script type="text/javascript" src="/SiteAssets/Scripts/jquery.min.js"></script>
<script type="text/javascript">
    $.ajax(
    {
        url: _spPageContextInfo.webAbsoluteUrl + "/_api/web?$select=custommasterurl", //THE ENDPOINT
        method: "GET",
        headers:
        {
            "Accept": "application/json; odata=verbose"
        },
        success: function(data)
        {
            //RESULTS HERE!!
            console.log('Custom Master URL: ' + data.d.CustomMasterUrl)
            alert('Custom Master URL: ' + data.d.CustomMasterUrl);

        }
    });
</script>

Add-in Code Snippet

The following code snippet is used in SharePoint Add-in to get the custom master page url of a SharePoint site. This returns a site relative url of a custom master page.

// Load the js files and continue to the successHandler
$.getScript(scriptbase + "SP.RequestExecutor.js", execCrossDomainRequest);

// Function to prepare and issue the request to get
// SharePoint data
function execCrossDomainRequest()
{
    // Initialize the RequestExecutor with the add-in web URL.
    var executor = new SP.RequestExecutor(appweburl);
    // Issue the call against the add-in web.
    // To get the CustomMasterUrl property using REST we can hit the endpoint:
    // appweburl/_api/web?select=CustomMasterUrl&@target=hostweburl
    // The response formats the data in the JSON format.
    executor.executeAsync(
    {
        url: appweburl + "/_api/SP.AppContextSite(@target)/web?$select=custommasterurl&@target='" + hostweburl + "'",
        method: "GET",
        headers:
        {
            "Accept": "application/json; odata=verbose"
        },
        success: successHandler,
        error: errorHandler
    });
}
// Function to handle the success event.
function successHandler(data)
{
    var jsonObject = JSON.parse(data.body)
    //jsonObject.d.CustomMasterUrl returns the server relative url of custom master page from the SharePoint site
    console.log('Custom master page URL: ' + jsonObject.d.CustomMasterUrl)
    alert('Custom master page URL: ' + jsonObject.d.CustomMasterUrl);
}

function errorHandler(data, errorCode, errorMessage)
{
    console.log("Could not complete cross-domain call: " + errorMessage);
}