Write SharePoint list items to text file using javascript/jquery

Iterate over all list items and collect the information.

var siteUrl = '/sites/MySiteCollection';

function retrieveListItems() {

var clientContext = new SP.ClientContext(siteUrl);
var oList = clientContext.get_web().get_lists().getByTitle('Announcements');

var camlQuery = new SP.CamlQuery();
camlQuery.set_viewXml('<View><Query><Where><Geq><FieldRef Name=\'ID\'/>' + 
    '<Value Type=\'Number\'>1</Value></Geq></Where></Query><RowLimit>10</RowLimit></View>');
this.collListItem = oList.getItems(camlQuery);

clientContext.load(collListItem);

clientContext.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceeded), Function.createDelegate(this, this.onQueryFailed));        

}

function onQuerySucceeded(sender, args) {

var listItemInfo = '';

var listItemEnumerator = collListItem.getEnumerator();

while (listItemEnumerator.moveNext()) {
    var oListItem = listItemEnumerator.get_current();
    listItemInfo += '\nID: ' + oListItem.get_id() + 
        '\nTitle: ' + oListItem.get_item('Title') + 
        '\nBody: ' + oListItem.get_item('Body');
}

alert(listItemInfo.toString());
}

function onQueryFailed(sender, args) {

alert('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());
}

Source

And here is a example to export a csv file (you should use a csv instead)

    function exportToCsv() {
        var myCsv = "Col1,Col2,Col3\nval1,val2,val3";

        window.open('data:text/csv;charset=utf-8,' + escape(myCsv));
    }

Source

You need to use ActiveX objects, you can write to text or excel files using ActiveX objects. Check out the below code for text files. The below JavaScript function shows an example of the same. For excel different ActiveX object is used.

function WriteFile() 
{
   var fso  = new ActiveXObject("Scripting.FileSystemObject");</br>

   var fh = fso.CreateTextFile("c:\\Test.txt", true); </br>
   fh.WriteLine("Some text goes here..."); 
   fh.Close(); 
}