为什么我的JavaScript Prime Number-Generator不起作用？

Question

The aim of this program is to list all the prime numbers from 1 up. 该程序的目的是列出从1开始的所有素数。 I am a complete novice. 我是一个完整的新手。 I began writing this in C++ (unsuccessfully) and translated to this (JS) I am aware of some problems but don't know how to solve them: handling global variables, writing replaces, no timeout before writing, etc. is it important that i use an external JS file? 我开始用C ++编写此程序（未成功），然后翻译成此（JS）。我知道一些问题，但不知道如何解决：处理全局变量，编写替换，编写前没有超时等是很重要的我使用外部JS文件？ In summary, how do i make this work? 总而言之，我该如何进行这项工作？

<!doctype html>
<html>
<head>
<script>

var number = 3; //to be run through the prime test
var prime = [2]; //numbers found to be prime
var found = 1; //counter for primes found
var runs = 0; //counter for times number has been tested
//numbers are tested against all smaller found primes
function test()
{
    window.scroll(0,document.height); //automatically view the latest prime
    var line = document.createElement("div");
    while(runs < found && (prime[runs] < (number / 2))) //has number passed all tests
    {
        if(number % prime[runs] !== 0) //is number divisible by smaller prime
        {
            runs = runs + 1; //number passed a test
        }
        else //number is not prime
        {
            number = number + 1; //next number generated
            runs = 0; //reset test counter for next number
            setTimeout(test, 100); //start running next number tests
        }
    } //number passed all tests
line.innerHTML = number; //prime number displayed
document.body.appendChild(line);
prime[found] = number; //prime number saved for testing
found = found + 1; //counter for found is increased
number = number + 1; //next number generated
runs = 0; //reset test counter for next number
setTimeout(test, 100); //start running next number tests
}

</script>
</head>
<body>
<form>
    <input type="button" onclick="test()">
</form>
</body>
</html>

Answer 1

A few things to note: 注意事项：

for (runs < found)

You appear to want a while loop here. 您似乎想要while此处循环。 for loops cannot consist just of a condition. for循环不能仅由条件组成。
document.writeln() cannot be used after the document has finished loading and has closed . 完成加载并关闭 document后，不能使用document.writeln() 。 Using them after this will re-open the document , resetting it to blank. 此后使用它们将重新打开document ，将其重置为空白。
To modify the DOM after this, you'll need to use innerHTML or document.createElement() and element.appendChild() . 要在此之后修改DOM，您需要使用innerHTML或document.createElement()和element.appendChild() 。
```
 var line = document.createElement('div'); line.innerHTML = number; document.body.appendChild(line); 
```
To avoid infinite recursion and give the UI thread a chance to update the display of the page, you can use a timer when calling test again: 为了避免无限递归并使UI线程有机会更新页面的显示，可以在再次调用test时使用计时器：
```
 setTimeout(test, 100); 
```

Answer 2

On the mathematical side, 在数学方面，

var prime = [1];

1 isn't a prime, and since 1 divides every number, 1不是质数，由于1除以每个数字，

while (runs < found) //has number passed all tests
{
    if (number % prime[runs] !== 0) //is number divisible by smaller prime
    {
        runs = runs + 1; //number passed a test
    }
    else //number failed a test
    {
        number = number + 1; //next number generated
        runs = 0; //reset test counter for next number
        setTimeout(test, 1000); //start running next number tests
    }
} //number passed all tests

always enters the else branch for runs = 0 . 总是进入else分支进行runs = 0 。

You can start with var prime = [2]; 您可以从var prime = [2]; or with var prime = []; 或使用var prime = []; and var found = 0; 并且var found = 0; . 。

为什么我的JavaScript Prime Number-Generator不起作用？

问题描述

2 个解决方案

解决方案1
0 2013-05-08 16:06:12

解决方案2
0 已采纳 2013-05-08 17:03:47

为什么我的JavaScript Prime Number-Generator不起作用？

问题描述

2 个解决方案

解决方案1 0 2013-05-08 16:06:12

解决方案2 0 已采纳 2013-05-08 17:03:47

解决方案1
0 2013-05-08 16:06:12

解决方案2
0 已采纳 2013-05-08 17:03:47