使用 JavaScript 获取位数 [英] Get number of digits with JavaScript

问题描述

正如我帖子的标题所暗示的那样，我想知道 var number 有多少个数字.例如:如果 number = 15; 我的函数应该返回 2.目前，它看起来像这样:

As the title of my post suggests, I would like to know how many digits var number has. For example: If number = 15; my function should return 2. Currently, it looks like this:

function getlength(number) {
  return number.toString().length();
}

但是 Safari 说由于 TypeError 无法正常工作:

But Safari says it is not working due to a TypeError:

'2' is not a function (evaluating 'number.toString().length()')

如您所见，'2' 实际上是正确的解决方案.但为什么它不是函数?

As you can see, '2' is actually the right solution. But why is it not a function?

推荐答案

length 是一个属性，而不是一个方法.你不能调用它，因此你不需要括号 ():

length is a property, not a method. You can't call it, hence you don't need parenthesis ():

function getlength(number) {
    return number.toString().length;
}

更新:正如评论中所讨论的，上面的示例不适用于浮点数.为了让它工作，我们可以用 String(number).replace('.', '').length 去掉句号，或者用正则表达式计算数字:String(number).match(/d/g).length.

UPDATE: As discussed in the comments, the above example won't work for float numbers. To make it working we can either get rid of a period with String(number).replace('.', '').length, or count the digits with regular expression: String(number).match(/d/g).length.

就速度而言，获取给定数字中位数的最快方法可能是数学计算.对于正整数，log10 有一个很棒的算法:

In terms of speed potentially the fastest way to get number of digits in the given number is to do it mathematically. For positive integers there is a wonderful algorithm with log10:

var length = Math.log(number) * Math.LOG10E + 1 | 0;  // for positive integers

对于所有类型的整数(包括负数)，@Mwr247 有一个出色的优化解决方案，但要小心使用 Math.log10，因为许多旧版浏览器不支持它.所以将 Math.log10(x) 替换为 Math.log(x) * Math.LOG10E 将解决兼容性问题.

For all types of integers (including negatives) there is a brilliant optimised solution from @Mwr247, but be careful with using Math.log10, as it is not supported by many legacy browsers. So replacing Math.log10(x) with Math.log(x) * Math.LOG10E will solve the compatibility problem.

由于众所周知的浮点数学行为，为十进制数创建快速数学解决方案并不容易，所以cast-to-string 方法将更容易和万无一失.正如 @streetlogics 所提到的，可以通过简单的数字到字符串的连接来完成快速转换，从而导致替换 要转换为的解决方案:

Creating fast mathematical solutions for decimal numbers won't be easy due to well known behaviour of floating point math, so cast-to-string approach will be more easy and fool proof. As mentioned by @streetlogics fast casting can be done with simple number to string concatenation, leading the replace solution to be transformed to:

var length = (number + '').replace('.', '').length;  // for floats

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