D3 Javascript plotting function

StackOverflow https://stackoverflow.com/questions/8387306

  •  28-10-2019
  •  | 
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سؤال

I am trying to write a tutorial about d3 and I found couple websites that can help but with not enough details.

I have the following code that outputs a bar chart: 

<html>
<head>
<div id="mainGraph">
        </div>
<script type="text/javascript" src="script.js"></script>
</head>
<body>
<script type="text/javascript">

var t = 1, // start time (seconds since epoch)
    v = 0, // start value (subscribers)
    data = d3.range(33).map(next); // starting dataset

 function next() {
   return {
    time: ++t,
     value: v = ~~Math.max(10, Math.min(80, Math.exp(t)))
   };
}
setInterval(function() {
   data.shift();
   data.push(next());
 }, 1500);

  var w = 40,
      h = 100;

  var x = d3.scale.linear()
      .domain([0, 1])
      .range([0, w]);

  var y = d3.scale.linear()
      .domain([0, 100])
     .rangeRound([0, h]);

     var chart = d3.select("body")
     .append("svg:svg")
     .attr("class", "chart")
     .attr("width", w * data.length + 10)
     .attr("height", h);

     chart.selectAll("rect")
     .data(data)
    .enter().append("svg:rect")
     .attr("x", function(d, i) { return x(i) + 5; })
     .attr("y", function(d) { return h - y(d.value) + 5; })
     .attr("width", w)
     .attr("height", function(d) { return y(d.value); });

     chart.append("svg:line")
     .attr("x1", 0)
     .attr("x2", w * data.length)
     .attr("y1", h + 5)
     .attr("y2", h + 5)
     .attr("stroke", "#000");





    </script>           
    </body>
    </html>

The first question is what does function()

the second question is when I try to change the set of data so i am trying to put v in function of t like v = Math.exp (t) this is not working and its giving me a black line only even though I changed the interval of max and min. Thank you.

هل كانت مفيدة؟

المحلول

function() as in :

setInterval(function() { ... });

is called a lambda function (or anonymus if you prefer). This means that the function has no name, and cannot be called outside it's scope. In this case, the setInterval function requires a function as parameter, so we send in the full function definition instead of just a reference to it.

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