Question

我是使用XMLHttpRequest的新手，我想我似乎遗漏了一些明显的东西-我有一个非常有效的URL，试图从中检索JSON数据，但是当我调用send on onerror函数时，但是onload没有（即使我得到了200）。您可以在此处查看测试页：https://pwas.resourcedata.com/walkipedia/webrequest.html

        function MakeWebRequest() {
        url = "https://data.wsdot.wa.gov/arcgis/rest/services/Shared/TownshipSection/MapServer/identify?geometry=-13606913.506613478%2C5937651.515662&geometryType=esriGeometryPoint&sr=&layers=all&layerDefs=&time=&layerTimeOptions=&tolerance=1&mapExtent=-13609094.35057674%2C5936620.810108784%2C-13602038.257402979%2C5939181.450556404&imageDisplay=400%2C300%2C96&returnGeometry=true&maxAllowableOffset=&geometryPrecision=&dynamicLayers=&returnZ=false&returnM=false&gdbVersion=&f=pjson";
        let xhr = new XMLHttpRequest();

        xhr.onload = function () {
            debugger;
            let data = JSON.parse(xhr.responseText);

        }

        xhr.onerror = function (x ) {
            alert("Error while calling Web API");
        }

        let httpVerb = "GET";

        xhr.open(httpVerb, url);

        xhr.setRequestHeader("Content-Type", "application/json");

        xhr.send();
    }

Answer 1

删除此行：

learnerRF = makeLearner("regr.ranger", par.vals = list("num.trees" = 5000)) 
parsRF = makeParamSet(
  makeIntegerParam("mtry", lower = 0 , upper = 10), 
)
tuneRF = makeTuneControlGrid() 
inner = makeResampleDesc("CV", iters = 10)
learnerRF = makeTuneWrapper(learnerRF, resampling = inner, par.set = parsRF,control = tuneRF, show.info = FALSE)

这是没有必要的，因为xhr.setRequestHeader("Content-Type", "application/json");请求没有任何内容（JSON在响应中）。并且触发了CORS验证错误。

如果您想指定只需要JSON响应，请使用：

GET

Answer 2

删除此行：

 xhr.setRequestHeader("Content-Type", "application/json");

请检查此小提琴的输出： https://jsfiddle.net/2e9jz6x3/2/

XMLHttpRequest在有效URL上引发错误

2 个答案: