I am working on something. But everytime I take away from the value, I have to refresh the page to show the new value.
localStorage.setItem("money", money - 20);
How do I make the value "money" refresh on the page without actually refreshing the page itself? Can it be done with pure JavaScript?
First things first, storing money in localStorage is not desirable. Users can easily change its value using developer tools. If you're using that value for caching, never trust that value in Backend.
Second, you have to update the value with custom function whenever you change the money and store it to localStorage. Like the following:
localStorage.setItem("money", money - 20);
document.getElementById("balance").innerText = localStorage.getItem("money") || 0;
localStorage is not supported in SO code snippet, so I'm going to post a full html here. You can just cut&paste and try to understand its logic.
Example:
<!DOCTYPE html>
<html>
<head>
<title>Balance Example</title>
</head>
<body>
<div>Balance: $<span id="balance">0</span></div>
<button id="btnWithdraw" onClick="withdraw(20)">Withdraw 20$</button>
<button id="btnDeposit" onClick="deposit(100)">Deposit 100$</button>
</body>
<script>
function getBalance() {
let money = parseFloat(localStorage.getItem("money") || 0);
return isNaN(money) ? 0 : money;
}
function setBalance(amount) {
localStorage.setItem("money", parseFloat(amount));
}
function withdraw(amount) {
let balance = getBalance();
if(balance < amount) {
return alert("Not enough balance!");
} else {
balance = balance - parseFloat(amount);
}
if (isNaN(balance)) balance = 0;
setBalance(balance);
renderBalance();
}
function deposit(amount) {
amount = parseFloat(amount);
if (isNaN(amount) || amount < 0) {
return alert("Invalid amount!");
}
let balance = getBalance();
balance += amount;
setBalance(balance);
renderBalance();
}
function renderBalance() {
document.getElementById("balance").innerText = getBalance().toFixed(2);
}
window.onload = function() {
renderBalance();
}
</script>
</html>
After updating localStorage, use document.getElementById() to select the element on your page that displays the value of your money variable and update its content with .innerHTML:
localStorage.setItem("money", money - 20);
document.getElementById("money").innerHTML = money - 20;
The following Pen shows a working example of how to implement this.
Show changed variable without reloading page on CodePen.
Related
I am second semester, taking a class in Javascript. Basically, we were given the HTML and CSS for a website, and it is supposed to do the following:
It's a number game. The computer generates a number, and you have ten tries to guess this number. If you get to zero, the computer wins, and there is a reset button which should reset all the variables and start again. Only problem is, I cannot for the life of me figure out how to reset the countDown variable after the score reaches 0. Please help. Also we are using only pure Javascript for this course for now. I don't want to cheat, I am more trying to figure out what the issue is that's holding me back.
var countDown = 10;
var computerNumber = Math.floor((Math.random() * 501) + 1);
function generate() {
playerNumber = document.getElementById("guess").value;
if (computerNumber == playerNumber && countDown > 0) {
alert("Congratulations! You've won!");
} else if (playerNumber < computerNumber && countDown > 0) {
countDown--;
document.getElementById("guesses").value = countDown;
document.getElementById("result").value = "Too Low";
} else if (playerNumber > computerNumber && countDown > 0) {
countDown--;
document.getElementById("guesses").value = countDown;
document.getElementById("result").value = "Too High";
} else if (countDown == 0) {
alert("Game Over. The Number Was " + computerNumber);
}
}
function reset() {
countDown = 10;
computerNumber = Math.floor((Math.random() * 501) + 1);
}
In the reset function, you would need to update the element that displays the countDown in the HTML
Here you need to add the reset button in the html:
<input type="button" class="reset-button" value="Reset Count">
Then grab that button in your JS below the reset function and attach an eventListener that fires the reset function when clicked:
const resetBtn = document.querySelector('.reset-button')
resetBtn.addEventListener('click', reset )
And that's it.
You would probably want the count displayed on the page, too. You could add a line in the reset function that pushes the new value of countDown into the html (with element.textContent = countDown.toString(), for example)
If you take a JS class in 2021 you should definitely use const and let instead of var, and let your teacher know why. Using var works, though, but will show a future employer that you're out of touch with what's going on in the JS world.
I'm writing a choose your own adventure program where If a specific option is chosen (example to wait) the user gets a random number between 1-10 to do push ups(the push-ups would be the user clicking on the prompt "ok" button however many times the random number is equal to) here's my code so far but I keep getting errors. I'm a complete noob so go easy on me.
var count = Math.floor((Math.random() * 10) + 1);
var setsOf10 = false;
function pushUps() {
alert("Nice! Lets see you crank out " + pushUps + "!");
}
if (setsOf10 == pushUp) {
alert("Nice! Lets see you crank out " + pushUp + "!");
setsOf10 = true;
}
for (var i=0; i<count; i++){
pushUps();
}
else {
alert("Really, thats it? Try again");
}
while ( setsOf10 == false);
}
After playing with this some more I can tell i'm close but still don't have it. and again, I'M NOT ASKING YOU TO SOLVE THIS FOR ME JUST NEED POINTERS AS TO WHAT IM DOING WRONG OR MISSING. Here's what I have, Its giving me my random number I just need it to allow me to click the "ok" button however many times the random number has assigned me.
var pushUpSets = Math.floor((Math.random() * 10) + 1);
function pushUps(){
alert(pushUpSets);
if (pushUpSets < 3){
var weak = "Thats it? Weak sauce!";
alert(weak);
}
else{
alert("Sweet lets get some reps in!");
}
for (i=0; i>3; i++){
pushUps(pushUpSets);
}
}
Here, the make a choice button is just dummy to allow us to go to do push ups. Each click decrements our count.
// This is important, we use this event to wait and let the HTML (DOM) load
// before we go ahead and code.
document.addEventListener('DOMContentLoaded', () => {
document.querySelector('#choice').addEventListener('click', makeChoice);
});
function makeChoice() {
// Call a method to set random pushups and setup the click event
setUpPushUp();
// Here we change the display style of the push up section so that it shows to the player.
document.querySelector('.activity').style.display = 'block';
}
// The pushups variable is declared at the document level
// This way our setUpPushUp and doPushUp functions have easy access.
let pushUps = 0;
function setUpPushUp() {
// Create a random number of pushups, in sets of 10.
// We add an extra 1 so we can call the doPushUp method to initialize.
pushUps = (Math.floor((Math.random() * 10)+1)*10)+1 ;
// Add a click event to the push up button and call our doPushUp method on each click.
document.querySelector('#push').addEventListener('click', doPushUp);
// This is just an init call, it will use the extra 1 we added and place test in our P tag.
doPushUp();
}
function doPushUp() {
// Get a reference to our output element, we will put text to player here.
let result = document.querySelector('p');
// They have clicked, so remove a push up.
pushUps--;
// See if the player has done all the required push ups (i.e. pushUps is 0 or less.)
if (pushUps > 0) {
result.innerText = `You need to crank out ${pushUps} pushUps`;
} else {
result.innerText = 'Nice work!';
}
}
.activity {
display: none;
}
<button id="choice">Make a choice !</button>
<div class="activity">
<p></p>
<button id="push">Push</button>
</div>
I'm trying to open build a system which opens a new link every time an anchor tag is clicked. I tried using random function but at times it opens the same link again and again. But whereas as I want the link to open in an order and follow the cycle.. That is if I have three links, the user clicking the anchor text first time will open the first link, then second, then third and later again the first link..
This means the link must change if a different user clicks.
Here is a code that I found which uses random function..
<script type="text/javascript'>
function random_3(){
var myrandom=Math.round(Math.random()*2)
var link1="http://www.codingforums.com"
var link2="http://www.cssdrive.com"
var link3="http://www.dynamicdrive.com"
if (myrandom==0)
window.location=link1
else if (myrandom==1)
window.location=link2
else if (myrandom==2)
window.location=link3
}
</script>
<form>
<input type="button" value="random link!" onClick="random_3()">
</form>
so can someone help me out with this?
I tried using random function but at times it opens the same link again and again
You're probably getting the same link several times in succession due to the random calculation that you're using.
Try the following instead:
var myrandom=Math.floor(Math.random()*3);
You should get a better distribution this way.
Now, regarding your original question, if you want a persistent state to be kept between page reloads, so that each time the link is different, you'll probably need to use cookies or localStorage for storing what was the last used index for that user.
Example:
var links = ['http://www.codingforums.com', 'http://www.cssdrive.com', 'http://www.dynamicdrive.com'];
function nextLink() {
var index = localStorage.getItem('lastPos') || -1;
index = (index + 1) % links.length;
localStorage.setItem('lastPos', index);
return links[index];
}
What you need to do is save the index of the link, and then increase it every time so that you cycle through the links in order.
Here's a working example of what you want:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width">
<title>JS Bin</title>
</head>
<body>
<script>
urls = ['http://domain1.com','http://domain2.com', 'http://domain3.com', 'http://domain4.com'];
var urlIndex = 0;
function openUrl(){
url = urls[urlIndex % urls.length];
window.location = url;
urlIndex ++;
}
</script>
Get a link
</body>
</html>
Here's a demo :)
First of all, you have to list your links in an array. Second, you have to define a variable that hold the last opened link's index in that array, to void a successive opening of the same link (indeed it's a URL). In general you may follow something like the following code:
urls = ['http://domain1.com','http://domain2.com', 'http://domain3.com', 'http://domain4.com'];
var lastUrl = '';
function getRandomIndex(arr){
return Math.floor(Math.random() * ((arr.length+1) - 1));
}
function openUrl(){
url = urls[getRandomIndex(urls)];
do {
if (url == lastUrl){
url = urls[getRandomIndex(urls)];
}
else{
lastUrl = url;
//Using alert instead of window.location for testing
alert(url)
//window.location = url;
}
}
while (lastUrl != url);
}
Then for test:
Click here for test
This is an online Demo
Reference: Generating random whole numbers in JavaScript in a specific range?
Edit
According your comment, the requirement is pretty easier, instead of choosing according to random value, you will define lastUrl as an integer store and every time the openUrl() is called, it will be increased by 1 after checking its value if it is greater than urls array length or not as follows:
Modified openUrl
urls = ['http://domain1.com','http://domain2.com', 'http://domain3.com', 'http://domain4.com'];
//lastUrl Index in urls array
// Global variable
var lastUrl = 0;
function openUrl(){
if (lastUrl > (urls.length - 1)){
//reset it to 0
lastUrl = 0;
}
else{
url = urls[lastUrl];
lastUrl++;
alert(url)
//window.location = url;
}
}
var myrandom = 0;
function random_3(){
myrandom += 1;
var link1="http://www.codingforums.com";
var link2="http://www.cssdrive.com";
var link3="http://www.dynamicdrive.com";
if (myrandom==1)
window.open('http://www.codingforums.com','_blank');
else if (myrandom==2)
window.open('http://www.cssdrive.com','_blank');
else if (myrandom==3)
window.open('http://www.dynamicdrive.com','_blank');
else if (myrandom>3)
window.open('http://www.codingforums.com','_blank');
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script>
<form>
<input type="button" value="random link!" onClick="random_3()">
</form>
You can count click like user click on button and basis on this manage.
What I’m trying to build Math testing app with JavaScript. But I’m having an issue with the FOR statement, what I want it to do is to add one point to the score for every question answered correct. To test it I have set the score to 0 and userID would be user input, if user enters the correct answer it would increase to 1 but it keeps increasing to 10. Is there a way to stop the count after the first cycle and wait till the second cycle and so forth till it hits 10?
<!doctype html>
<html>
<head>
</head>
<body>
<div id="scoreBlock"><span id="score">0</span></div>
<input type="text" id="userID"/>
<button onclick="begin();">Start</button>
<script>
function begin(){
var h= document.getElementById("score");
var user =document.getElementById("userID").value;
var test = "5";
for(h=0;h<=10;h++){
if(user==="5"){
document.getElementById("score").innerHTML= h;
}else if(!user==="5"){
alert("noting");
}
}//end of while
}//end of function
</script>
</body>
</html>
In this test you consider the right answer happens when user == 5. You do it 10 times while not changing the conditions. So obviously it's 10 time the right answer.
<script>
function begin(){
var user = document.getElementById("userID").value;
var test = "5";
var correctAnswer = 0;
for(var h=0;h<=10;h++){
if(user==="5"){
correctAnswer++;
}
}
document.getElementById("score").innerHTML= correctAnswer;
if (correctAnswer == 0) {
alert("noting");
}
</script>
If I understand your question correctly, you want the score to be updated every time the user clicks the button and checks if the value of user is the same as test. In that case, you don't need a For loop.
<script>
var score = 0;
var test = "5";
function begin(){
var user = document.getElementById("userID").value;
if(user === test) {
score++;
}
document.getElementById("score").innerHTML= score;
}
</script>
Someone at work jokingly sent out an email with a html file intended to crash your browser that was the following
<html>
<script type="text/javascript">
function crash(){
for(i=0;i<5000000001;i++){
document.write(i);
}
}
</script>
<body onload="crash();">
</body>
</html>
Anyways it doesn't do a great job of it in Chrome and a conversation arose that it created a friendly competition to see who could write javascript to make a page count to 5,000,000,000 as quickly as possible without causing the browser to become unresponsive or crash.
I came up with the following piece of javascript that is intended to be used in Chrome.
<html>
<script type="text/javascript">
function countToFiveBillion(counter, num){
if(num < 5000000000)
{
num++;
if(num % 18700 == 0){
counter.innerHTML = num;
setTimeout(function() {countToFiveBillion(counter, num)}, 1);
} else {
countToFiveBillion(counter, num);
}
}
}
function initiateCountDown()
{
var counter = document.getElementById("counter");
var num = +counter.innerHTML;
countToFiveBillion(counter, num);
}
</script>
<body onload="initiateCountDown();">
<div id="counter">0</div>
</body>
</html>
The reason that this will only run in chrome is that I'm using the setTimeout call to avoid creating a stackoverflow in chrome. (Chrome also allows you the largest stack for recursive calls out of all of the browsers).
Is there any way for me to make this count any quicker? I think that I can increase the amount counted a little before it causes an overflow (somewhere less than 100 though) The only stipulation is that is has to display as many numbers as possible as it counts.
Improved Code:
<html>
<script type="text/javascript">
var counter;
var num = 0;
function countToFiveBillion(){
if(num < 5000000000)
{
num++;
if(num % 18701 == 0){
setTimeout("countToFiveBillion()", 1);
counter.value = num;
} else {
countToFiveBillion();
}
} else {
counter.value = "number greater than 5 Billion";
}
}
function initiateCountDown()
{
counter = document.getElementById('counter');
countToFiveBillion();
}
</script>
<body onload="initiateCountDown();">
<input type="text" id="counter" value="0" />
</body>
</html>
Made count and element globabl
Switched to text input instead of div
moved update UI to after setting the callback
Don't use .innerHTML = ... to display the number. According to this test, setting the value property of an input element is more efficient.
<input type="text" id="counter" value="0" />
Instead of constructing a new function, I recommend to use global / local variables, and passing a function reference as an argument to setTimeout, or use setInterval at init.
Swap setTimeout("countToFiveBillion()",1) for setTimeout(countToFiveBillion,0).
Explanation: "countToFiveBillion()" is inefficient; First, the string gets converted to a function and called, then another function call follows. The suggested function runs only has to call a function, without creating new ones. It's also called a split second faster.
Lift the limit (I was able to increase 18701 to 20000). After lifting the limit to such a rounded number, I noticed that the counter value is updated between each time-out.
Fixed some errors in the implementation (replaced .innerHTML with .value at the else-block).
Relevant code:
<input type="text" id="counter" />
<script>
var counter, num = 0;
function countToFiveBillion(){
if(num < 5e9)
{
if(++num % 18701 == 0){
setTimeout(countToFiveBillion, 0);
counter.value = num;
} else {
countToFiveBillion();
}
} else {
counter.value = "number greater than 5 Billion";
}
}
function initiateCountDown(){
counter = document.getElementById('counter');
counter.value = num; //Init, show that the script is
countToFiveBillion();
}
window.onload = initiateCountDown;
</script>
Fiddle: http://jsfiddle.net/KTtae/
Webworker example, index.html
<!DOCTYPE HTML>
<html>
<head>
<title>5 billion</title>
</head>
<body>
<input type="text" id="counter" value="0" />
<script type="text/javascript" charset="utf-8">
var
iCounter = document.getElementById('counter')
, counter = new Worker('worker.js');
iCounter.value = 0;
counter.addEventListener('message', function (e) {
iCounter.value = e.data;
}, false);
</script>
</body>
</html>
worker.js:
for (var i = 0; i < 5e9; i++) {
if (i % 18701 === 0) {
postMessage(i);
}
}
The counting can be splited in multiple workers if needed.