Error while pdating Master Page through JavaScript Client Object Model using SP 2013 App

Question

I have created a Site Collection in SharePoint 2013 online.

In this site I am trying to update Master Page through JavaScript Client Object Model. My JQuery scripts are able to change the Site Master page as well as System Master Page. I can validate the change under Site Settings  Master Page (under Look and Feel section).

I am able to execute the script successfully without any error. But when I refresh my home page, it redirects me to error page saying “File Not Found” Error and it gives one correlation ID. When I change any setting in Master Page and save it, my site again looks good.

code which I am using:

//context = new SP.ClientContext.get_current();
//var site = clientContext.get_site();
//var web = context.get_site();

context = new SP.ClientContext.get_current();
var web = context.get_site().get_rootWeb();
context.load(web, 'ServerRelativeUrl');
web.set_customMasterUrl('/_catalogs/masterpage/seattle.master');
web.set_masterUrl('/_catalogs/masterpage/seattle.master');
web.update();

I tried with commented code also for trial... Would appreciate if someone could give me some direction here.....

Answer 1

Perfectly working Code:

$(document).ready(function () {
    jQuery('.cmdSet').click(function () {

        var scriptBase = _spPageContextInfo.webAbsoluteUrl + "/_layouts/15/";

        $.getScript(scriptBase + "sp.runtime.js", function () {

            $.getScript(scriptBase + "sp.js", function () {

                $.getScript(scriptBase + "sp.core.js", sharePointReady);

            });
        });

    });
});



    // create page-level variables to hold client context and web
    var context;
    var web;
    var masterurl;
    var site;
    function sharePointReady() {

    // assign values to page-level variables
    context = new SP.ClientContext.get_current();
    web = context.get_web();

    // provide CSOM with instructions to load info about current web


    context.load(web, 'ServerRelativeUrl');
    web.set_customMasterUrl(L_Menu_BaseUrl + '/_catalogs/masterpage/seattle.master');
    web.set_masterUrl(L_Menu_BaseUrl + '/_catalogs/masterpage/seattle.master');
    web.update();

    context.executeQueryAsync(function () {

        alert("Starting Master Page Setting......");
        masterurl = web.get_serverRelativeUrl() + "/_catalogs/masterpage/seattle.master";
        alert(masterurl);
        alert("Master Page is Set Successfully!!!");

    }, function (sender, args) {

        alert("Error: " + args.get_message());

    });
}

Answer 2

Get your server relative url using _spPageContextInfo

var customMasterPage = "custom.v15.master";
var siteRelativeUrl = _spPageContextInfo.siteServerRelativeUrl;

web.set_customMasterUrl(siteRelativeUrl + '/_catalogs/masterpage/' + customMasterPage);
web.set_masterUrl(siteRelativeUrl + '/_catalogs/masterpage/' + customMasterPage);
web.update();