NodeJS Can't Access Variable Inside Callback

问题

I believe this is a problem with it being async, but I do not know the solution.

    PagesController.buy = function() {

  var table="";
  Selling.find({}, function(err, res) {
    for (var i in res) {
      console.log(res[i].addr);
      table = table + "res[i].addr";
    }
  });
  this.table = table;
  console.log(table);
  this.render();
}

My issue is that this.table=table is returning undefined if I try access it outside of the function, and I cannot figure out how to display the table on the page.

回答1:

The problem is the Selling.find is asynchronous and likely isn't complete by the time the this.table = table is executed. Try something like the following.

PagesController.buy = function() {
  var that = this;
  Selling.find({}, function(err, res) {
    var table = '';
    for (var i in res) {
      console.log(res[i].addr);
      table = table + res[i].addr;
    }

    that.table = table;
    console.log(table);
    that.render();
  });
}

That will guarantee that table isn't used until after the results have been fetched and table has been populated.

来源：https://stackoverflow.com/questions/16471548/nodejs-cant-access-variable-inside-callback