Javascript math.round 与 parseInt

math.round vs parseInt

提问by Chris

Have a quick JS question. What is the difference between math.round and parseInt?

有一个快速的 JS 问题。math.round 和 parseInt 有什么区别？

I made a JS script to sum the inverses of prompted numbers:

我做了一个 JS 脚本来求和提示数字的倒数：

    <script type="text/javascript">
    var numRep = prompt("How many repetitions would you like to run?");
    var sum = 0; 
    var count = 0;
    var i = 1;     //variable i becomes 1


    while (i <= numRep)  {//  repeat 5 times

       var number = prompt("Please enter a non zero integer");

       if(number==0){
         document.write("Invalid Input <br>");
 count++;
       }
       else{
          document.write("The inverse is: " + 1/number + "<br>");
          sum = sum + (1/parseInt(number));  //add number to the sum
       }

       i++; //increase i by 1
    }

    if (sum==0){
    document.write("You did not enter valid input");}
    else { document.write("The sum of the inverses is: " + sum);  //display sum
    }
    </script></body></html>

and it uses parseInt. If I wanted to makeit use math.round, is there anything else I need to do so that It knows to limit the number of decimal places accordingly?

它使用 parseInt。如果我想让它使用 math.round，还有什么我需要做的，以便它知道相应地限制小数位数？

In other words, does math.round have to be formatted in a certain way?

换句话说， math.round 是否必须以某种方式格式化？

回答by Tim Morgan

The two functions are really quite different.

这两个功能真的很不一样。

parseInt()extracts a number from a string, e.g.

parseInt()从字符串中提取一个数字，例如

parseInt('1.5')
// => 1

Math.round()rounds the number to the nearest whole number:

Math.round()将数字四舍五入到最接近的整数：

Math.round('1.5')
// => 2

parseInt()can get its number by removing extra text, e.g.:

parseInt()可以通过删除多余的文本来获取其编号，例如：

parseInt('12foo')
// => 12

However, Math.round will not:

但是， Math.round 不会：

Math.round('12foo')
// => NaN

You should probably use parseFloatand Math.roundsince you're getting input from the user:

您可能应该使用parseFloat并且Math.round因为您从用户那里获得输入：

var number = parseFloat(prompt('Enter number:'));
var rounded = Math.round(number);

回答by locrizak

Math.roundwill round the number to the nearest integer. parseIntwill assure you that the value is a number

Math.round将数字四舍五入到最接近的整数。parseInt将向您保证该值是一个数字

So what you will need is something like this:

所以你需要的是这样的：

number = parseInt(number);

if ( isNan(number) || number == 0 ){
    document.write("Invalid Input <br>");
    count++;
}

This will assure you that the use has put in a number

这将向您保证使用已经输入了一个数字

回答by Jakub Konecki

Math.roundexpects a number, parseIntexpects a string.

Math.round需要一个数字，parseInt需要一个字符串。

Use parseInt('12345', 10)for parsing 10-based numbers.

使用parseInt('12345', 10)解析为基础的10个号码。

http://www.javascripter.net/faq/convert2.htm

http://www.javascripter.net/faq/convert2.htm