这是我第一次使用JS，需要使用jQuery和Chart Js来绘制时间序列。但是我不断收到以下错误：
Uncaught TypeError: Cannot read property 'top' of undefined
at callFllSamplesApi (plot.js:105)
//Script included before body tag (Chart.js 2.4, jQuery 3.4, local file plot.js with callFllSamplesApi() )
<body>
<canvas id="line-chart" width="450" height="500"></canvas>
<button id="btn1" onclick="callFllSamplesApi()">Generate FLL Graph</button>
</body>
下面显示函数FLFLampamplesApi的功能，并抛出错误。
function callFllSamplesApi() {
var request = new XMLHttpRequest()
request.open('GET', 'http://193.142.33.4/api/samples', true)
request.onload = function(){
... Parsing code
}
request.send()
var ctx = document.getElementById("line-chart");
var myChart = new Chart(ctx, { <- Line 105 which throws an error
... More code for plotting
}
}
});
}
您在折线图元素上缺少getContext()