HTML：元描述标签的用途(HTML: Meta description tag's uses)

 你的承诺链是一团糟，你的意图远非清晰，所以这是一个基于你的代码松散的例子，以展示你如何使事情更容易理解。 
 
$.ajax({url: '/echo/json'}) //do one request
    .then(function(resultFromServer){
            //yay! 1st request was successful
            return $.ajax({url: '/echo/json'}); //then do another request
        },function(err){
            //something went wrong with the AJAX

            //rethrow to let the next "catch" pick this up, skipping further "then" clauses
            throw err;
        })
    .then(function(resultFromServer) {
            rec.price=999.99; //yay! success again
            //...
        },function() {
            //something went wrong
        });

Your promise chain is a mess, and your intent is far from clear, so here's an example, loosely based on your code, to demonstrate how you might make things a little easier to understand.
 
$.ajax({url: '/echo/json'}) //do one request
    .then(function(resultFromServer){
            //yay! 1st request was successful
            return $.ajax({url: '/echo/json'}); //then do another request
        },function(err){
            //something went wrong with the AJAX

            //rethrow to let the next "catch" pick this up, skipping further "then" clauses
            throw err;
        })
    .then(function(resultFromServer) {
            rec.price=999.99; //yay! success again
            //...
        },function() {
            //something went wrong
        });