当值被复制时，在JavaScript If语句中返回false

Question

我有一个JS语句，它每30秒通过Ajax获取数据。我希望我的if语句的方式是，如果具有相同值的变量名已经被处理，它将不再处理它。例如，如果var名称John已经被处理过，它就不会再处理它。

有人有办法解决这个问题吗？

ajax_call = function() {
  $.ajax({
    type: "GET",
    url: "test.php",
    dataType: "JSON",
    success: function(response) {

      var len = response.length;
      for (var i = 0; i < len; i++) {
        var name = response[i].name;
        var size = response[i].size;

      }

      var one = "6-8";

      if (size == one && name != name) {
        person.val++;
        person.value = person.val;

      } else {
        console.log("name already exist");
      }
    }
};
var interval = 30000;
setInterval(ajax_call, interval);
});

Answer 1

正如注释中提到的，您将需要在$.ajax函数作用域之外的变量，在成功时更新该变量，并重新检查下一个$.ajax调用。目前，每次$.ajax触发success:中的vars时，都会使用新的response数据进行重置。

在本例中，我使用new Set()对象添加/存储名称，并检查名称是否存在，这样，如果let processed = new Set();存储对象中不存在名称，则可以执行魔术。

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set

请参阅下面代码中的注释(未测试).

// constant variable ajax_call_interval
const ajax_call_interval = 30000;

// updatable variable processed set object for storing processed names
let processed = new Set();

// updatable bool check variable ajax_call_running
let ajax_call_running = false;

// ajax call function
function ajax_call() {

  // update ajax_call_running var to bool true
  ajax_call_running = true;

  // jquery ajax call
  $.ajax({
    type: "GET",
    url: "test.php",
    dataType: "JSON",
    success: function(response) {

      // great success 
      console.log("success");

      // loop through response json as key / data
      $.each(response, function(key, data) {

        // if processed set object has data.name already
        if (processed.has(data.name)) {

          // log name already exists
          console.log("name already exists in processed");

          // this will skip to the next json data item in this jquery each loop

        // else if name does exist in processed set object then...  
        } else {

          // add new name to processed set object var for use in next ajax call
          processed.add(data.name);

          // log name added to processed
          console.log("new name added to processed");

          // do your other magic here for unprocessed name json data
          // ...
          let name = data.name;
          let size = data.size;

        }

      });

      // i am assuming the below should run once the above jquery each function has completed looping through your json response

      // update ajax_call_running var to bool false
      ajax_call_running = false;

      // re-run our ajax call in 30000 ms
      ajax_call_runner(ajax_call_interval);

    },
    error: function(error) {

      // oh no 
      console.log("error");

      // do error response stuff here...

      // update ajax_call_running var to bool false
      ajax_call_running = false;

      // re-run our ajax call in 30000 ms anyway
      ajax_call_runner(ajax_call_interval);

    }

  });

}

// ajax call runner function with interval ms param
function ajax_call_runner(interval) {

  // set time out interval for ajax runner
  setTimeout(function() {

    // if ajax call is not running then
    if (!ajax_call_running) {

      // fire the ajax call
      ajax_call();

    }

  // interval time ms using parent function param
  }, interval);

}

// shorthand for $(document).ready()
$(function() {

  // run our ajax call in 1 ms
  ajax_call_runner(1);

});