javascript - 使用异步请求初始化对象

Question

这是我的对象定义:

function DrilledLayer(sourceLayerName, sourceTableName, targetLayerName, targetFieldName, operators, baseLayer=false) {
        this.sourceLayerName = sourceLayerName;
        this.sourceTableName = sourceTableName;
        this.targetLayerName = targetLayerName;
        this.targetFieldName = targetFieldName;
        this.operators = operators;
        this.baseLayer = baseLayer;
        this.targetLayerId;
        this.drilledLayerId;
        this.selectedCode;
        this.redraw = false;

        this.getTargetLayerId(); //this function must initialize this.targetLayerId
}

DrilledLayer.prototype.getTargetLayerId = function(){
  $.soap({
    url: 'https://url/version_4.8/services/MapService',
    method: 'getLayersIdByName',
    appendMethodToURL: false,
    data : {
        mapInstanceKey: mapKey,
        layerName: this.targetLayerName,
    },
    error: function(){
        alert("error getLayersIdByName");
    },
    success: function(soapResponse){
        layerId = soapResponse.toJSON().Body.getLayersIdByNameResponse.getLayersIdByNameReturn.getLayersIdByNameReturn.text;
        this.targetLayerId = layerId;
    }
  });
}

这就是我创建对象的方式:

drillCs = new DrilledLayer("Drilled CS", "Cs_Franco_General.TAB", "RA_General", "Code_RA", "=")

如果我查看drillCs对象，没有定义targetLayerId属性，但我知道soap请求已成功发出。为什么？

Answer 1

JavaScript 中的

this 主要是通过调用函数的方式来设置的。 success 回调期间的 this 不会与调用 getTargetLayerId 函数期间的 this 相同，您一定要记住。

在这种情况下，最简单的方法可能是使用变量:

DrilledLayer.prototype.getTargetLayerId = function(){
  var layer = this;                     // <=== Set it
  $.soap({
    url: 'https://url/version_4.8/services/MapService',
    method: 'getLayersIdByName',
    appendMethodToURL: false,
    data : {
        mapInstanceKey: mapKey,
        layerName: this.targetLayerName,
        },
    error: function(){
        alert("error getLayersIdByName");
     },
    success: function(soapResponse){
        layerId = soapResponse.toJSON().Body.getLayersIdByNameResponse.getLayersIdByNameReturn.getLayersIdByNameReturn.text;
        layer.targetLayerId = layerId; // <=== Use it
        }
    });
}

更多(在我的博客上):

• You must remember this

当然，在异步回调触发之前(这将在 new 调用返回后的一段时间)，您不会正确看到，但您似乎对异步方面感到满意的这个。