javascript - 如何使用javascript从动态创建的html元素中获取输入数据

Question

我有一个动态创建的字段集，其中包含一个表单和 6 个用于姓名、联系人等的输入。我想使用以下内容从这些输入字段中获取数据：

document.getElementsByClassName("input-field")[0].id.value;

但无论我使用什么方法访问元素（ById、ByTagName 等），我总是得到错误无法获取未定义的值。为什么当我有 6 个具有相同类名的输入字段时它未定义，我如何访问该值？谷歌搜索了很长时间，找不到任何有用的东西。

编辑

这是我的代码

// get body tag
var mainBody = document.getElementsByTagName("body");

// create array of input labels
var inputNameValues = ["first-name", "last-name", "title", "health-num", "email", "telephone"];
var inputLabels = ["First Name", "Last Lame", "Title", "Health Authority Number", "Email", "Telephone (Optional)"];

// create the contact form
var contactPageDiv = document.createElement("div");
contactPageDiv.setAttribute("id", "form-cointainer");
var fieldSet = document.createElement("fieldset");
fieldSet.setAttribute("id", "contact-form")
var form = document.createElement("form");
form.setAttribute("onsubmit", validateForm());
fieldSet.appendChild(form);
// create labels and input fields
for (let i = 0; i < inputLabels.length; i++) {
  var label = document.createElement("label");
  var bold = document.createElement("b");
  var inputText = document.createTextNode(inputLabels[i]);
  bold.appendChild(inputText);
  label.appendChild(bold);
  form.appendChild(document.createElement("br"));
  var input = document.createElement("input");
  input.setAttribute("class", "input-field");
  input.setAttribute("type", "text");
  input.setAttribute("id", inputNameValues[i]);

  // setup placeholder text, focus and required fields
  input.setAttribute("placeholder", inputLabels[i]);
  if (inputNameValues[i] === "first-name") {
    input.setAttribute("autofocus", "true");
  }
  if (inputNameValues[i] !== "telephone") {
    input.setAttribute("required", "true");
  }

  // add tool tip icon
  if (inputNameValues[i] === "health-num") {
    // create the img
    var img = document.createElement("img");
    img.setAttribute("id", "question-mark");
    img.setAttribute("src", "resources/questionmark.jpg");
    img.setAttribute("alt", "question mark symbol");

    // create the tool tip text box
    var textBox = document.createElement("div");
    textBox.setAttribute("id", "tool-tip-text-box");
    var paragraph = document.createElement("p");
    textBox.appendChild(paragraph);
    var text = document.createTextNode("If you do not know your ZHA number, please contact your GP");
    paragraph.appendChild(text);
    label.appendChild(textBox);
    img.onmouseover = function() {
      textBox.style.display = "block";
    }
    img.onmouseout = function() {
      textBox.style.display = "none";
    }
    label.appendChild(img);
  }
  form.appendChild(label);
  form.appendChild(input);
}
// create submit button
var submitBtn = document.createElement("input");
submitBtn.setAttribute("id", "submit-btn");
submitBtn.setAttribute("type", "submit");
submitBtn.setAttribute("value", "Submit!");
form.appendChild(submitBtn);
contactPageDiv.appendChild(fieldSet);

// display the form on the page
mainBody[0].appendChild(contactPageDiv);

function validateForm() {

  console.log(document.getElementsByClassName("input-field")[0].value);

}

标签： javascriptdom

Answer 1

这是一个 X/Y 问题

删除 () 从form.setAttribute("onsubmit", validateForm());

它在字段存在之前立即执行

也使用 eventListener

form.addEventListener("submit", validateForm);

我推荐 querySelector

function validateForm(e) {
  e.preventDefault(); // remove when you have tested

 // takes the first - use querySelectorAll to get the rest
  console.log(document.querySelector(".input-field").value); 
}

// get body tag
var mainBody = document.getElementsByTagName("body");

// create array of input labels
var inputNameValues = ["first-name", "last-name", "title", "health-num", "email", "telephone"];
var inputLabels = ["First Name", "Last Lame", "Title", "Health Authority Number", "Email", "Telephone (Optional)"];

// create the contact form
var contactPageDiv = document.createElement("div");
contactPageDiv.setAttribute("id", "form-cointainer");
var fieldSet = document.createElement("fieldset");
fieldSet.setAttribute("id", "contact-form")
var form = document.createElement("form");
form.addEventListener("submit", validateForm);
fieldSet.appendChild(form);
// create labels and input fields
for (let i = 0; i < inputLabels.length; i++) {
  var label = document.createElement("label");
  var bold = document.createElement("b");
  var inputText = document.createTextNode(inputLabels[i]);
  bold.appendChild(inputText);
  label.appendChild(bold);
  form.appendChild(document.createElement("br"));
  var input = document.createElement("input");
  input.setAttribute("class", "input-field");
  input.setAttribute("type", "text");
  input.setAttribute("id", inputNameValues[i]);

  // setup placeholder text, focus and required fields
  input.setAttribute("placeholder", inputLabels[i]);
  if (inputNameValues[i] === "first-name") {
    input.setAttribute("autofocus", "true");
  }
  if (inputNameValues[i] !== "telephone") {
    input.setAttribute("required", "true");
  }

  // add tool tip icon
  if (inputNameValues[i] === "health-num") {
    // create the img
    var img = document.createElement("img");
    img.setAttribute("id", "question-mark");
    img.setAttribute("src", "resources/questionmark.jpg");
    img.setAttribute("alt", "question mark symbol");

    // create the tool tip text box
    var textBox = document.createElement("div");
    textBox.setAttribute("id", "tool-tip-text-box");
    var paragraph = document.createElement("p");
    textBox.appendChild(paragraph);
    var text = document.createTextNode("If you do not know your ZHA number, please contact your GP");
    paragraph.appendChild(text);
    label.appendChild(textBox);
    img.onmouseover = function() {
      textBox.style.display = "block";
    }
    img.onmouseout = function() {
      textBox.style.display = "none";
    }
    label.appendChild(img);
  }
  form.appendChild(label);
  form.appendChild(input);
}
// create submit button
var submitBtn = document.createElement("input");
submitBtn.setAttribute("id", "submit-btn");
submitBtn.setAttribute("type", "submit");
submitBtn.setAttribute("value", "Submit!");
form.appendChild(submitBtn);
contactPageDiv.appendChild(fieldSet);

// display the form on the page
mainBody[0].appendChild(contactPageDiv);