How do I get the sum of items of several document libraries using JavaScript

Question

I have document library A, document library B and document library C. Every library has kinda many items in it. Now I would like to have a counter, which counts the amount of all items and makes a sum out of it. I'm searching for a JavaScript solution for this, so that I can display the amount of items for example in a Content Editor Web Part on any other Site of the same Site Collection.

Answer 1

I answered a similar question here.

Your JavaScript would look similar to this (note the use of jQuery):

var count = 0;

$.when(
    RestGet("listname1", "yourErrorDiv", "Couldn't get from listname1"),
    RestGet("listname2", "yourErrorDiv", "Couldn't get from listname2"),
    RestGet("listname3", "yourErrorDiv", "Couldn't get from listname3")).done(function () {
        // Output results to screen, e.g.:        
        yourdiv.html(count);
    });

// @listName, the name of the list to pull data from
// @errorDiv, a string containing the ID attribute of the DIV that the error message should be displayed in. If this is ommitted, no error message will be displayed on the page
// @errorMessage, a string containing the error message that should be displayed if the call fails
function RestGet(listName, errorDiv, errorMessage) {
    var dfd = $.Deferred();
    $.ajax({
        url: _spPageContextInfo.webAbsoluteUrl + "/_api/web/lists/getbytitle('" + listName + "')/items",
        type: "GET",
        headers: {
            "accept": "application/json;odata=verbose",
        },
        success: function (data) {
            count = count + data.d.results.length;
            dfd.resolve();
        },
        error: function (data) {
            $(String.format("[id='{0}']", errorDiv)).html(message + " Check your browser's console for details of the error.");
            console.log(JSON.stringify(data));
            dfd.reject();
        }
    });
    return dfd;
}