How to use JavaScript to fill a form on another page
You're trying to maintain state between pages. Conventionally there are two ways to maintain state:
- Store state in cookies
- Store state in the query string
Either way your first page has to persist state (to either cookies or the query string) and the other page has to - separately - restore the state. You can't use the same script across both pages.
Example: Using Cookies
Using cookies, the first page would have to write all the form data you'll need on the next page to cookies:
<!DOCTYPE html>
<html>
<head>
<title>Maintaining State With Cookies</title>
</head>
<body>
<div>
Setting cookies and redirecting...
</div>
<script>
// document.cookie is not a real string
document.cookie = 'form/title=My Name is Richard; expires=Tue, 29 Aug 2017 12:00:01 UTC'
document.cookie = 'form/text=I am demoing how to use cookies in JavaScript; expires=Tue, 29 Aug 2017 12:00:01 UT';
setTimeout(function(){
window.location = "./form-cookies.html";
}, 1000);
</script>
</body>
</html>
... and the second page would then read those cookies and populate the form fields with them:
<!DOCTYPE html>
<html>
<head>
<title>Maintaining State With Cookies</title>
</head>
<body>
<form id="myForm" action="submit.mumps.cgi" method="POST">
<input type="text" name="title" />
<textarea name="text"></textarea>
</form>
<script>
var COOKIES = {};
var cookieStr = document.cookie;
cookieStr.split(/; /).forEach(function(keyValuePair) { // not necessarily the best way to parse cookies
var cookieName = keyValuePair.replace(/=.*$/, ""); // some decoding is probably necessary
var cookieValue = keyValuePair.replace(/^[^=]*\=/, ""); // some decoding is probably necessary
COOKIES[cookieName] = cookieValue;
});
document.getElementById("myForm").getElementsByTagName("input")[0].value = COOKIES["form/title"];
document.getElementById("myForm").getElementsByTagName("textarea")[0].value = COOKIES["form/text"];
</script>
</body>
</html>
Example: Using the Query String
In the case of using the Query String, the first page would just include the query string in the redirect URL, like so:
<!DOCTYPE html>
<html>
<head>
<title>Maintaining State With The Query String</title>
</head>
<body>
<div>
Redirecting...
</div>
<script>
setTimeout(function(){
window.location = "./form-querystring.html?form/title=My Name is Richard&form/text=I am demoing how to use the query string in JavaScript";
}, 1000);
</script>
</body>
</html>
...while the form would then parse the query string (available in JavaScript via window.location.search - prepended with a ?):
<!DOCTYPE html>
<html>
<head>
<title>Maintaining State With The Query String</title>
</head>
<body>
<form id="myForm" action="submit.mumps.cgi" method="POST">
<input type="text" name="title" />
<textarea name="text"></textarea>
</form>
<script>
var GET = {};
var queryString = window.location.search.replace(/^\?/, '');
queryString.split(/\&/).forEach(function(keyValuePair) {
var paramName = keyValuePair.replace(/=.*$/, ""); // some decoding is probably necessary
var paramValue = keyValuePair.replace(/^[^=]*\=/, ""); // some decoding is probably necessary
GET[paramName] = paramValue;
});
document.getElementById("myForm").getElementsByTagName("input")[0].value = GET["form/title"];
document.getElementById("myForm").getElementsByTagName("textarea")[0].value = GET["form/text"];
</script>
</body>
</html>
Example: With a Fragment Identifier
There's one more option: since state is being maintained strictly on the client side (not on th server side) you could put the information in a fragment identifier (the "hash" part of a URL).
The first script is very similar to the Query String example above: the redirect URL just includes the fragment identifier. I'm going to re-use query string formatting for convenience, but notice the # in the place where a ? used to be:
<!DOCTYPE html>
<html>
<head>
<title>Maintaining State With The Fragment Identifier</title>
</head>
<body>
<div>
Redirecting...
</div>
<script>
setTimeout(function(){
window.location = "./form-fragmentidentifier.html#form/title=My Name is Richard&form/text=I am demoing how to use the fragment identifier in JavaScript";
}, 1000);
</script>
</body>
</html>
... and then the form has to parse the fragment identifier etc:
<!DOCTYPE html>
<html>
<head>
<title>Maintaining State With The Fragment Identifier</title>
</head>
<body>
<form id="myForm" action="submit.mumps.cgi" method="POST">
<input type="text" name="title" />
<textarea name="text"></textarea>
</form>
<script>
var HASH = {};
var hashString = window.location.hash.replace(/^#/, '');
hashString.split(/\&/).forEach(function(keyValuePair) {
var paramName = keyValuePair.replace(/=.*$/, ""); // some decoding is probably necessary
var paramValue = keyValuePair.replace(/^[^=]*\=/, ""); // some decoding is probably necessary
HASH[paramName] = paramValue;
});
document.getElementById("myForm").getElementsByTagName("input")[0].value = HASH["form/title"];
document.getElementById("myForm").getElementsByTagName("textarea")[0].value = HASH["form/text"];
</script>
</body>
</html>
And if you can't edit the code for the form page
Try a greasemonkey script.
It is a good place to use cookies
Ex: From quirksmode.org
function createCookie(name,value,days) {
if (days) {
var date = new Date();
date.setTime(date.getTime()+(days*24*60*60*1000));
var expires = "; expires="+date.toGMTString();
}
else var expires = "";
document.cookie = name+"="+value+expires+"; path=/";
}
function readCookie(name) {
var nameEQ = name + "=";
var ca = document.cookie.split(';');
for(var i=0;i < ca.length;i++) {
var c = ca[i];
while (c.charAt(0)==' ') c = c.substring(1,c.length);
if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length,c.length);
}
return null;
}
and a side note, you can use the onload event to know when the page is ready
<script language="javascript">
function setTitle(){
var title = prompt("Field Info","Default Value");
var form = document.form[0];
form.elements["fieldName"].value = title;
}
windows.onload = setTitle;
</script>