d3提供了为元素赋值的方法:datum(),data(), enter(),exit()
datum() ：是给单个元素赋值，与select()连用
<!DOCTYPE html>
<html>
<head>
<script type = "text/javascript" src = "https://d3js.org/d3.v4.min.js"></script>
</head>
<body>
<div>111</div>
<script>
d3.select("div")
.datum("aaaa")
.text(function(d) {
return "Created new paragraph element and the data " + d + " is assigned.";
});
</script>
</body>
</html>
data()：是给多个元素赋值，与selectAll()连用
<html>
<head>
<script type = "text/javascript" src = "https://d3js.org/d3.v4.min.js"></script>
</head>
<body>
<p></p>
<p></p>
<div></div>
<script>
d3.selectAll("p")
.data(["aaa","bbbb"])
.text(function(d) {
return "Created new paragraph element and the data " + d + " is assigned.";
});
</script>
</body>
</html>
enter()：当data 设置的数值与选择的元素不匹配（设置的数值多）的情况 将多出的数值预设置在其中，后边用appden去添加相应的元素，来展示 也是与data，selectAll连用(该方法是给超出的预设元素赋值，不超出的是不会设置值的)
<!DOCTYPE html>
<html>
<head>
<script type = "text/javascript" src = "https://d3js.org/d3.v4.min.js"></script>
</head>
<body>
<ul id="list">
</ul>
<script>
d3.select("#list").selectAll("li")
.data([2,3,4])
.enter()
.append("li")
.text(function(d) { return "This is dynamically created element and the value is " + d; });
</script>
</body>
</html>
<!DOCTYPE html>
<html>
<head>
<script type = "text/javascript" src = "https://d3js.org/d3.v4.min.js"></script>
</head>
<body>
<ul id="list">
<li>111</li>
<li>222</li>
<li></li>
<li></li>
</ul>
<script>
d3.select("#list").selectAll("li")
.data([2,3,4,2,3,1])
.enter()
.append("li")
.text(function(d) { return "This is dynamically created element and the value is " + d; });
</script>
</body>
</html>
输出值为
- 111
- 222
- This is dynamically created element and the value is 3
- This is dynamically created element and the value is 1
exit():返回与data不匹配的元素，可以用来删除这些元素