bit4fox - 1 year ago 90
Javascript Question

# Get number of digits with JavaScript

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();
}
``````

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

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

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

`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;
}
``````

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`.

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
``````

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.

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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