JavaScript代碼在回調中無效

Question

在以下JavaScript代碼中，如果warnBeforeNew為false，則文件打開代碼有效。 但是，如果warnBeforeNew為true，則不會出現錯誤“Uncaught TypeError：無法讀取未定義的屬性'root'”。

我不知道這是否與范圍有關，但如何讓文件加載代碼在回調中工作？ 謝謝。

Editor.prototype.open = function(path) {
  if (Editor.warnBeforeNew==true){
    this.showDialog({
        dialogLabel: 'You have unsaved changes. Are you sure you want to discard them and open a different file?',
        submitLabel: 'Discard',
        cancelLabel: 'Cancel',
        submitCallback: function() {
          Editor.warnBeforeNew=false;
          this.filesystem.root.getFile(path, {}, this.load.bind(this), error.bind(null, "getFile " + path));
        }
    });
  } else {
    this.filesystem.root.getFile(path, {}, this.load.bind(this), error.bind(null, "getFile " + path));
  }
};

Answer 1

你要保存的價值this是因為，當回調被調用時，它與不同的接收器比外部函數：

if (Editor.warnBeforeNew==true){
    var thing = this; // choose a more meaningful name if possible...
    this.showDialog({
        dialogLabel: 'You have unsaved changes. Are you sure you want to discard them and open a different file?',
        submitLabel: 'Discard',
        cancelLabel: 'Cancel',
        submitCallback: function() {
          Editor.warnBeforeNew=false;
          thing.filesystem.root.getFile(path, {}, thing.load.bind(thing), error.bind(null, "getFile " + path));
        }
    });
  } else {
    this.filesystem.root.getFile(path, {}, this.load.bind(this), error.bind(null, "getFile " + path));
  }

Answer 2

嘗試在回調中捕獲范圍並使用它。

Editor.prototype.open = function(path) {
var that=this;
  if (Editor.warnBeforeNew==true){
    this.showDialog({
        dialogLabel: 'You have unsaved changes. Are you sure you want to discard them and open a different file?',
        submitLabel: 'Discard',
        cancelLabel: 'Cancel',
        submitCallback: function() {
          Editor.warnBeforeNew=false;
          that.filesystem.root.getFile(path, {}, that.load.bind(that), error.bind(null, "getFile " + path));
        }
    });
  } else {
    this.filesystem.root.getFile(path, {}, this.load.bind(this), error.bind(null, "getFile " + path));
  }
};

Answer 3

您的showDialog方法的submitCallback也需要綁定 - 它訪問this.filesystem.root.…失敗。

this.showDialog({
    …,
    submitCallback: function() {
      Editor.warnBeforeNew=false;
      this.filesystem.root.getFile(path, {}, this.load.bind(this), error.bind(null, "getFile " + path));
    }.bind(this)
//    ^^^^^^^^^^
});