Javascript infinite loop in prompt
Question
So i have just made a simple HTML page in which a JS script runs when the page loads. But the problem is that it just goes infinite after asking password. I tried to find some solutions but failed to do the same. Please help. Below is the code.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Alert test</title>
</head>
<body onload="alert()">
<script>
function alert() {
var uname, pass, corr_uname = "admin", corr_pass = "admin";
while(!uname) {
uname = prompt("Enter Username: ");
}
while(!pass) {
pass = prompt("Enter Password: ");
}
if((uname == corr_uname) && (pass == corr_pass)) {
alert("Access Granted!!");
} else {
alert("Access Denied!");
alert();
}
}
</script>
<h1>Welcome!</h1>
</body>
</html>
The funny thing is that when i run the same code (JS runs after clicking a button) in W3Schools, it just works fine!!
2 answers
solution1
3 ACCPTED 2022-05-03 18:29:19
The problem is that you have created a function named alert which already exists in javascript, so you are calling it recursively and infinitely.
Solution fix
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Alert test</title>
</head>
<body onload="alert2()">
<script>
function alert2() {
var uname, pass, corr_uname = "admin", corr_pass = "admin";
while(!uname) {
uname = prompt("Enter Username: ");
}
while(!pass) {
pass = prompt("Enter Password: ");
}
if((uname == corr_uname) && (pass == corr_pass)) {
alert("Access Granted!!");
} else {
alert("Access Denied!");
myFunction();
}
}
</script>
<h1>Welcome!</h1>
</body>
</html>
I renamed your functional alert to alert2 .
Kindly accept it as answer if it works for you, thanks!
solution2
1 2022-05-03 19:03:54
JavaScript had mutable built-in functions so your alert function overwrites the native alert and every alert call becomes recursive in a never ending loop.
Besides renaming the function, there's no need to use a while loop since prompt stalls execution. You can use uname && to invalidate the username if the user cancels the username prompt.
There's also no need to use <body onload="??"> if you just put the script within <head>...</head>
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Alert test</title>
<script>
const corr_uname = "admin", corr_pass = "admin";
function authenticate() {
const uname = prompt("Enter Username: ");
const pass = uname && prompt("Enter Password: ");
const isCredentialsValid = uname == corr_uname && (pass == corr_pass);
const accessType = isCredentialsValid ? 'Granted' : 'Denied';
alert(`Access ${accessType}!!`);
}
authenticate();
</script>
</head>
<body>
<h1>Welcome!</h1>
</body>
</html>
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