md`# US COVID-19 Daily Tested Cases（美国 COVID-19 每天检测数曲线）`
md`
US COVID-19 Daily Tested Cases
本线状图用于显示每天美国 COVID-19 的每天测试量的线状图曲线我们使用的是在线 JSON 数据，数据是通过 AWS 进行读取的。
你可以直接访问下面的链接来获得我们处理上传的数据。
https://cdn.ossez.com/dataset/json/covid19/covid19-daily-tested-us.json
虽然我们每天都会自动上传一些数据，但是你可能的更新数据每次都不一样。
我们主要也是希望通过 Observablehq 这个平台来学习 D3 图表的使用。`
chart = {
const svg = d3.create("svg")
.attr("viewBox", [0, 0, width, height]);
svg.append("g")
.call(xAxis);
svg.append("g")
.call(yAxis);
svg.append("path")
.datum(data)
.attr("fill", "none")
.attr("stroke", "steelblue")
.attr("stroke-width", 1.5)
.attr("stroke-linejoin", "round")
.attr("stroke-linecap", "round")
.attr("d", line);
return svg.node();
}
parseTime = d3.timeParse("%Y%m%d");
line = d3.line()
.defined(d => !isNaN(d.value))
.x(d => x(parseTime(d.date)))
.y(d => y(d.value))
x = d3.scaleUtc()
.domain(d3.extent(data, d => parseTime(d.date)))
.range([margin.left, width - margin.right])
y = d3.scaleLinear()
.domain([0, d3.max(data, d => d.value)]).nice()
.range([height - margin.bottom, margin.top])
xAxis = g => g
.attr("transform", `translate(0,${height - margin.bottom})`)
.call(d3.axisBottom(x).ticks(width / 80).tickSizeOuter(0))
yAxis = g => g
.attr("transform", `translate(${margin.left},0)`)
.call(d3.axisLeft(y))
.call(g => g.select(".domain").remove())
.call(g => g.select(".tick:last-of-type text").clone()
.attr("x", 3)
.attr("text-anchor", "start")
.attr("font-weight", "bold")
.text(data.y))
margin = ({top: 20, right: 30, bottom: 30, left: 40})
height = 500
d3 = require("d3@5")
Purpose-built for displays of data
Observable is your go-to platform for exploring data and creating expressive data visualizations. Use reactive JavaScript notebooks for prototyping and a collaborative canvas for visual data exploration and dashboard creation.
