[英]Javascript; html form; user input; display input
我無法弄清楚為什么此代碼不會顯示用戶輸入的信息。 我需要讓用戶從 html 表單輸入信息,將此信息添加到數組中,然后顯示信息(實際上,需要做的不止這些,但無法超越這一點)。 我需要輸入的信息顯示在頁面上。 謝謝
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Homework 10</title>
<script type="text/javascript">
//Variables for arrays
var fName = [];
var lName = [];
var tScore = [];
//Variables from user input
var fNameInput = document.getElementById("firstName");
var lNameInput = document.getElementById("lastName");
var tScoreInput = document.getElementById("testScore");
//Variable for display
var display = document.getElementById("display");
//Function to add user info to arrays
function insert() {
fName.push(fNameInput.value);
lName.push(lNameInput.value);
tScore.push(tScoreInput.value);
clearAndShow();
}
//Function to display info entered from array
function clearAndShow() {
fNameInput.value = "";
lNameInput.value = "";
tScoreInput.value = "";
display.innerHTML = "";
display.innerHTML += "First Name: " + fName.join(", ") + "<br/>";
display.innerHTML += "LastName: " + lName.join(", ") + "<br/>";
display.innerHTML += "Test Score: " + tScore.join(", ") + "<br/>";
}
</script>
</head>
<body bgcolor="Cornsilk">
<h2>Average Student Scores</h2>
<form>
<fieldset>
<legend><strong>Enter First, Last Name and Test Score:</strong></legend><br />
<input type="text" id="firstName" placeholder="First name"/><p />
<input type="text" id="lastName" placeholder="Last name"/><p />
<input type="number" id="testScore" placeholder="Test Score"/><p />
<input type="button" value="Save/Show Average" onclick="insert()"/><p />
</fieldset><p />
</form>
<div id="display"></div>
</body>
</html>
我試圖運行代碼。 我有一個錯誤
test.html:23 Uncaught ReferenceError: fName is not defined
您可以通過在函數內移動變量聲明來解決這個問題。
//Variables for arrays
var fName = [];
var lName = [];
var tScore = [];
//Function to add user info to arrays
function insert() {
var fNameInput = document.getElementById("firstName");
var lNameInput = document.getElementById("lastName");
var tScoreInput = document.getElementById("testScore");
fName.push(fNameInput.value);
lName.push(lNameInput.value);
tScore.push(tScoreInput.value);
clearAndShow();
}
//Function to display info entered from array
function clearAndShow() {
var display = document.getElementById("display");
var fNameInput = document.getElementById("firstName");
var lNameInput = document.getElementById("lastName");
var tScoreInput = document.getElementById("testScore");
fNameInput.value = "";
lNameInput.value = "";
tScoreInput.value = "";
display.innerHTML = "";
display.innerHTML += "First Name: " + fName.join(", ") + "<br/>";
display.innerHTML += "LastName: " + lName.join(", ") + "<br/>";
display.innerHTML += "Test Score: " + tScore.join(", ") + "<br/>";
}
原因是當初始聲明發生時元素不存在。
主要問題是 Javascript 在 HTML 之前加載。 結果,當 Javascript 嘗試查找具有元素“firstName”的元素時,它無法找到它,因為它尚未加載。
要解決此問題,您應該將 script 標記移到 body 標記下方,以便在 Javascript 訪問 HTML 之前加載 HTML。
作為一個額外的好處,它縮短了頁面加載時間,因為瀏覽器在呈現 HTML 之前不必等待 JavaScript 加載
示例代碼:
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>Homework 10</title> </head> <body bgcolor="Cornsilk"> <h2>Average Student Scores</h2> <form> <fieldset> <legend><strong>Enter First, Last Name and Test Score:</strong></legend><br /> <input type="text" id="firstName" placeholder="First name"/><p /> <input type="text" id="lastName" placeholder="Last name"/><p /> <input type="number" id="testScore" placeholder="Test Score"/><p /> <input type="button" value="Save/Show Average" onclick="insert()"/><p /> </fieldset><p /> </form> <div id="display"></div> </body> <script type="text/javascript"> //Variables for arrays var fName = []; var lName = []; var tScore = []; //Variables from user input var fNameInput = document.getElementById("firstName"); var lNameInput = document.getElementById("lastName"); var tScoreInput = document.getElementById("testScore"); //Variable for display var display = document.getElementById("display"); //Function to add user info to arrays function insert() { fName.push(fNameInput.value); lName.push(lNameInput.value); tScore.push(tScoreInput.value); clearAndShow(); } //Function to display info entered from array function clearAndShow() { fNameInput.value = ""; lNameInput.value = ""; tScoreInput.value = ""; display.innerHTML = ""; display.innerHTML += "First Name: " + fName.join(", ") + "<br/>"; display.innerHTML += "Last Name: " + lName.join(", ") + "<br/>"; display.innerHTML += "Test Score: " + tScore.join(", ") + "<br/>"; } </script> </html>
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