1、選擇元素
現在有一段html檔案，body中有三個段落元素

    <p>Apple</p>
    <p id="myid" class="myClass">pear</p>
    <p class="myClass">banana</p>

• 選擇第一個p
  d3.select("body").select("p")

• 選擇三個p
  d3.select("body").selectAll("p")

• 選擇第二個p
  d3.select("body").select("#myid").style("color","red")

• select the second p and third p
  d3.select("body").selectAll(".myClass")

2、insert or append element

• append() :add elements in the end of election

//add element p in the end of every p
d3.select("body").select("p").
    append("p").text(" the element of appended")

//only add one p in the end of
 
 body
body.append("P").text("add p in the end of body")

• insert()

body.insert("p").text("insert p in the head of body")

3.remove element

d3.select("body").select("#removeId")
    .remove()