Develop Reference

How do I generate a random X value for each "projectile" in my falling objects game using Javascript?

I am coding a game that is currently in its very early stages for a project to try to learn more about coding. In my game, objects generate randomly (green squares), and the player (red square), avoids them. I am having trouble trying to get the green squares to generate from a random position on the x-axis. I already have a formula to generate a random number for X, but after it selects a number randomly, all the "projectiles" generate there, rather than all generating from a different area. How would I get all the "projectiles" to generate from different positions on the x-axis randomly?
var randomX = Math.floor(Math.random() * 480) + 15;
function updateGameArea() {
var x, y;
for (i = 0; i < projectiles.length; i += 1) {
if (player.crashWith(projectiles[i])) {
gameArea.stop();
return;
}
}
gameArea.clear();
gameArea.frameNo += 1;
if (gameArea.frameNo == 1 || everyinterval(150)) {
x = randomX;
y = gameArea.canvas.height;
projectiles.push(new component(40, 40, "green", x, y));
}
for (i = 0; i < projectiles.length; i += 1) {
projectiles[i].y += -1; // the shape is using its coordinates to build downward from its y position
projectiles[i].update();
}
player.newPos();
player.update();
}
function everyinterval(n) {
if ((gameArea.frameNo / n) % 1 == 0) {return true;}
return false;
Expected: Green squares generate in random positions on the x- axis every 3 seconds and move upwards
Actual: Green squares all generate from the same random position on the X-axis.

You should reset X every time you're adding a new projectile:
if (gameArea.frameNo == 1 || everyinterval(150)) {
randomX = Math.floor(Math.random() * 480) + 15;
x = randomX;
y = gameArea.canvas.height;
projectiles.push(new component(40, 40, "green", x, y));
}
Otherwise, the randomX value stays constant as the value originally evaluated on line 1 when the interpreter reached it.

Here's your problem:
var randomX = Math.floor(Math.random() * 480) + 15;
// Generates a random number and stores it to randomX
// Called using 'randomX'
You need to turn it into a function if you want it to run each time:
var randomX = function() { Math.floor(Math.random() * 480) + 15 };
// Returns a new number each time
// Called using 'randomX()'

Both shivashriganesh mahato and natelouisdev have, essentially responded to how to fix the issue but since you are learning coding here is a tip. When you code, the code will run in a particular order. If you want something to be reassigned repeatedly, in this case a randomized number being used, and you want it to occur only after an event, you need to make sure that it gets trigger within each event.
natelouisdev has a good approach because, by using it as a function, you can call your randomizer more cleanly in your code and make it reassign the value of x each time.
Since you are building a game, it is also a good idea to compartmentalize your code. It'll make it easier to keep your ideas in order for each event trigger.
Example:
function gameLoss(){} - Define event return upon game loss. You can
then create editable rules to reason for loss without having to edit
the loss
function gameActive(){} - Defines what is normal gameplay. everything that occurs during normal gameplay should be managed here.
function gameArea(){} - Defines game canvas that function more for UI than for gameplay (scores, lifes, size of screen, etc)
Had you created individual functions you'd realize you only need a randomized 'x' value upon regular play thus you'd assign it within the gameActive() function and not as a global variable. Then you'd call the gameActive() function as many times as needed within a time interval to ensure a unique value is created each time.
-Side note: Don't litter unnecessary global variables. It'll make a mess off of your code when debugging. -

JavaScript and Array's

EDIT I originally posted this with my version of the J.S but it's so far off no one can even help so i'm starting over. Here is the pseudocode i have done that needs to be translated into a Javascript program. Any help is appreciated!
I am a beginning programmer i understand this code will have multiple errors, that's why i am here. Array's and loops have given me much trouble while trying to learn them and especially with formatting them in JavaScript. The things i know are incorrect or still need i commented out i still need them, i also know i'm not passing anything i just can't seem to wrap my head around how to get them there. I'm also not sure if while gather input i'm using alter and prompt correctly. In the display function the spacing is necessary for when it will be displayed. Corrections and explanations are greatly appreciated.
Module main()
//Declare local variables
Declare endProgram = “no”
While endProgram == “no”
Declare Real notGreenCost[12]
Declare Real goneGreenCost[12]
Declare Real savings[12]
Declare String months[12] = “January”, “February”, “March”, “April”, “May”, “June”, “July”, “August”, “September”, “October”, “November”, “December”
//function calls
getNotGreen(notGreenCost, months)
getGoneGreen(goneGreenCost, months)
energySaved(notGreenCost, goneGreenCosts, savings)
displayInfo(notGreenCost, goneGreenCosts, savings, months)
Display “Do you want to end the program? Yes or no”
Input endProgram
End While
End Module
Module getNotGreen(Real notGreenCost[], String months[])
Set counter = 0
While counter < 12
Display “Enter NOT GREEN energy costs for”, months[counter]
Input notGreenCosts[counter]
Set counter = counter + 1
End While
End Module
Module getGoneGreen(Real goneGreenCost[], String months[])
Set counter = 0
While counter < 12
Display “Enter GONE GREEN energy costs for”, months[counter]
Input goneGreenCosts[counter]
Set counter = counter + 1
End While
End Module
Module energySaved(Real notGreenCost[], Real goneGreenCost[], Real savings[])
Set counter = 0
While counter < 12
Set savings[counter] = notGreenCost[counter] – goneGreenCost[counter]
Set counter = counter + 1
End While
End Module
Module displayInfo(Real notGreenCost[], Real goneGreenCost[], Real savings[], String months[])
Set counter = 0
While counter < 12
Display “Information for”, months[counter]
Display “Savings $”, savings[counter]
Display “Not Green Costs $”, notGreenCost[counter]
Display “Gone Green Costs $”, goneGreenCost[counter]
End While
End Module

A few notes:
Currently the program creates a few variables and functions that
don't seem to interact
Most of the edits below are not optimal - there are parts that
could be done by much simpler means (i.e. counter++) - But thats
for you to learn =P
I made quite a few assumptions of what you wanted the program to
do, they might be wrong, they might be right
var notGreenCost = []; //Array lengths don't need to be specified
var goneGreenCost = [];
var savings = [];
var months = ["January", "Feburary", "March", "April", "May", "June"];
//A boolean value (true | false) would suit this better as opposed to "yes"/ "no"
var endProgram = false;
var option = 0;
/* You dont need main functions in javascript
* migrated everything to be global :/
* Delete:
function main(){
// Move this (made it global): var endProgram = "no";
}
*/
// I don't think this is meant to be initMonths..
// Maybe something like getOptions?
function /*initMonths*/getOptions(){
while (endProgram == false){ //lowercase while
//Because prompt would block everything else until it gets input
//we probably want to move the prompt to be after the alerts
alert("options:"); //Clarity
alert("1 to enter data");
alert("2 to display data");
alert("3 to write data to a file");
alert("4 to read data from a file");
//Alter global "option" to take the value of the prompt
option = prompt("What would you like to do? Type:");
//} //I assume you want the rest of the code in this while loop - otherwise it will loop forever
// Delete this bracket (its unmatched): {
// Delete return statement as it will stop the function return option;
// Delete this bracket (its unmatched): }
//Create a variable to take the value of prompt (this should be outside the while loop) but it seem clearer for explanation purposes to be here
var toEnd;
toEnd = prompt("Do you want to end the program (enter yes or no)");
// Javascript uses != for "not equal to" and && for "AND"
while (toEnd != "no" && toEnd != "yes") {
toEnd = prompt("Please enter a value of yes or no");
}
//I think you want to assign the value of toEnd to endProgram
// Note the the below is not the only/best way to do it
if(toEnd == "no") {
endProgram = false;
} else if(toEnd == "yes") {
endProgram = true;
}
// While use brackets not End s
// End While
// End While
}//End while loop here
}
Javascript in a browser cannot alter files - writeToFile, readFromFile have all been removed
I believe you want months to be global, if it is then initMonths is unnecessary
getNotGreen:
function getNotGreen(){
//You don't need to specify types in Javascript
/*Integer*/ var counter = 0
while (counter < 6){ //lowercase while
//I'm assuming you want to combine the values of "Enter NOT GREEN energy costs for" and months[counter] - This is done by using the + sign
//Im also assuming you want to read the value into notGreenCost
//.push adds a value to a array
notGreenCost.push(prompt("Enter NOT GREEN energy costs for" + months[counter]))
//Returning here makes the rest of the function redundant
//}
//return notGreenCost[counter];
//}
//Javascript does not use Set
// Note that below is not the only/best way to do it
/*Set*/ counter = counter + 1
} //End the while loop here
}
getGoneGreen:
function getGoneGreen(){
//Counter should probably be local (not global) - use var
var counter = 0;
while (counter < 6){//lowercase while
//I'm assuming you want to combine the values of "Enter NOT GREEN energy costs for" and months[counter] - This is done by using the + sign
//Im also assuming you want to read the value into notGreenCost
//.push adds a value to a array
goneGreenCost.push(prompt("Enter GONE GREEN energy costs for" + months[counter]));
//See above (getNotGreen)
//}
//return goneGreenCost[counter];
/*Set*/ counter = counter + 1;
}//End while loop here
}
energySaved:
function energySaved(){
//Counter should probably be local (not global) - use var
var counter = 0;
while (counter < 6){//lowercase while
savings[counter] = notGreenCost[counter] - goneGreenCost[counter]
counter = counter + 1;
}
} //I assume you want to end energySaved here?
displayInfo:
function displayInfo(){
//Alert produced individual boxes, i assume you want the following in a single window?
// "\n" is a line break
alert("SAVINGS NOT GREEN GONE GREEN MONTH\n"+
"_________________________________________________\n");
//Counter should probably be local (not global) - use var
var counter = 0;
while (counter < 6){//lowercase while
alert( "$" + savings[counter] + "$" + notGreenCost[counter] + "$" + goneGreenCost[counter] + "" + months[counter]);
counter = counter + 1;
}
} //I assume you want to end displayInfo here?

referenceerror treasureHunter not defined?

so i was programming a javascript program, and for some reason, i got an error saying: ReferenceError: treasureHunter not defined
I searched all over the internet for this info, but although this has been answered many times, their answers don't fit specifically to the problem in the code.
Here's the code:
// Sets a global variable for loot. Global variables exist outside functions or conditional statements. Local variables exist within those things.
global loot = 0;
// alert(loot);
// Creates a function called treasureHunter(). We don't put anything in the parenthesis, but we will later for other functions.
function treasureHunter() {
//Creates a local variable inside treasureHunter called treasureSuccess equal to Math.random(). Math.random is bult into JavaScript, and creates a random number between 0 and 1, e.g. .456 or .99. We use this to create excitement in an otherwise dull and boring existence.
var treasureSuccess = Math.random();
//Here we create a local variable called closedChest equal to the image that we want to pull down from the interwebs when we fail at getting loot.
var closedChest = "<img src='https://s-media-cache-ak0.pinimg.com/736x/eb/c7/84/ebc784ae55857b1470767c4747eb0715.jpg' length='285px' width='285px'>";
//Here we create a local variable called openChest equal to the image that we want to call up when we succeed - YES!
var openChest = "<img src='https://slm-assets1.secondlife.com/assets/1545906/lightbox/e6cfd0355756301c0f6f6d666e75c3de.jpg?1277247329' length='285px' width='285px'>";
var dragon = "<img src='http://orig06.deviantart.net/dd94/f/2012/112/c/b/cb9da88db9660edea4746e95df8fa4ed-d4x7orn.jpg' length='285px' width='285px'>";
//Here we create a conditional statement that asks if the variable treasureSuccess is greater than 5. This is called a boolean operation, it can be answered yes or no. This will of course be random, since treasureSuccess is equal to Math.random() - see above.
if (treasureSuccess > .5) {
//Here we tell the conditional statement what to do if it evaluates true, in other words, if Math.random() happens to be greater than .5. This will change the element using treasureChest, our DIV above in our HTML to the openChest variable, which is set to the image of an open chest. Go figure :)
if (treasureSuccess > .9) {
//dragon time!!
document.getElementById("TreasureChest").innerHTML = dragon;
//dragon image
loot = 0;
//loot reset
document.getElementById("Loot").innerHTML = "You lost all your gold!";
}
}
else {
document.getElementById("TreasureChest").innerHTML = openChest;
//This adds 100 to the global variable loot, each time we are successful, or each time treasureSuccess is greater than .5
loot = loot + 100;
//This tells the loot ID selector to update, so we can see how much gold we've got. THis uses the updated value for loot, which is why it is written below the loot = loot +100 line.
document.getElementById("Loot").innerHTML = "You've got" + " " + loot + " " + " gold";
//waits 500 milliseconds
setTimeout(treasureHunter,500);
document.getElementById("TreasureChest").innerHTML = closedChest;
//reputs the picture
}
//this is the end of the conditional statement
//This tells the statement what to do if the conditional statement evaluates to false, or if treasureSuccess is less than .5. You get a chest slammed shut in your face son.
else document.getElementById("TreasureChest").innerHTML = closedChest;
}
//this is the end of the function
I call it like this:
<div onclick="treasureHunter()" align="center" id="TreasureChest">
<img src="https://s-media-cache-ak0.pinimg.com/736x/eb/c7/84/ebc784ae55857b1470767c4747eb0715.jpg" length="285px" width="285px">
Any help is appreciated!

There are some syntax errors, so treasureHunter() wasn't defined.
global in global loot = 0; doesn't seem valid. Change it to var or something.
else in else document.getElementById("TreasureChest").innerHTML = closedChest; is invalid since there are no corresponding if. Remove it or fix the code properly.

How to call a function every 1-3 second?

My goal is to write a mini-game using canvas, one of the task is to create "bug" object entering the scene between every 1-3 seconds. I did try functions like setTimeOut,setInterval but I couldn't get it right. Here is my attempt
bugs =[];
function addBug(){
var bug = createBug();
bugs.push(bug);
}
function createRandomNumber(max){
return Math.floor((Math.random() * max) + 1);
};
var enterBug = setInterval(addBug,createRandomNumber(10)*1000);
currently I got it spawning at constant rate but don't know how to change it to every 1-3.Any suggestion? thanks in advance.

Currently, you are only setting the rate once at initial setInterval call. You would likely need to use setTimeout like this:
...
function addBug(){
...
bugTimeout = setTimeout(addBug, createRandomNumber(10)*1000);
}
...
bugTimeout = setTimeout(addBug, createRandomNumber(10)*1000);
You also may think about your random number generation if you want to get more randomness. Right now you can only get exact second values 1-10 since you are multiplying by 1000 to convert to seconds AFTER the random generation is done. If you want something more random you might use:
function createRandomNumber(maxSeconds){
minSeconds = 1;
if (maxSeconds < minSeconds) {
maxSeconds = minSeconds;
}
interval = maxSeconds - minSeconds;
return (Math.floor(Math.random() * interval) + minSeconds) * 1000;
};
You of course would not need to multiply by 1000 anymore when setting timeout.
bugTimeout = setTimeout(addBug, createRandomNumber(10))

How to add multiples of a number and overwrite previous entry using js timing?

I am trying to create a function that continuously adds the same number to itself. Or simply displays multiples of one number every so many seconds with the setInterval method.
For now, let's just say I want to display multiples of ten.
I know how to get a regular while loop to simply display multiples of ten in a row, but what I want to do here is continually replace the previous text every time the function is called. I am trying to create a game and this is going to be the experience calculator. So it needs to display the total experience earned over the given time.
I was trying something along the lines of this:
window.setInterval(
function writeExp ()
{
var j;
while (rounded > 0)
{
var i = w*10;
var j = j + i;
}
document.getElementByID("exp").innerHTML=j;
}, experience)
This seems logical enough to me, but obviously something is wrong, as it does not work. I have tried googling various things like how to sum numbers in javascript or continuously sum, among others, but it is somewhat difficult to word to get it more centered to my needs. So this is the best way to get my questions answered.

There are lot of undefineds in your code, but general example would be
var interval = 1000,
result = 0,
elem = document.getElementByID("exp");
window.setInterval(function () {
result *= 10;
elem.innerHTML = result;
}, interval);
or without global variables
var interval = 1000,
multiply = function (elem) {
var result = 0;
return function () {
result *= 10;
elem.innerHTML = result;
}
};
window.setInterval(multiply(document.getElementByID("exp")), interval);