JavaScript：Number（）的预期行为

Question

I'm currently reading string integers from files and passing them to functions. Since most files have a trailing line feed, I was wondering about the behavior of Number() .

To get the max_pid variable from a RHEL kernel file, I'm using an asynchronous read.

var options = {
  encoding: 'utf8'
};

fs.readFile('/proc/sys/kernel/pid_max', options, function (err, data) {
  var max_pid = Number(data);

  // or trim the string first
  var max_pid = Number(data.trim());
});

The variable data for my system returned the string '32768\\n' , and using Number() on that string strips the line feed. Is this the intended behavior of Number() , or should I be using str.trim() on the variable before passing it to Number() ?

I ask this for reasons of consistency across environments, as well as proper use of functions.

Answer 1

According to Section 9.3.1 of the ECMAScript specification , conversion of a string to a number will automatically strip leading and trailing white space. I'd be shocked if there was a JavaScript engine that did not conform to this part of the spec. The call to trim() is unnecessary (but harmless).

Answer 2

Whitespace is automatically trimmed from the start and end of strings. It won't remove whitespace from the middle of a number, eg, "12 345" (evaluates to NaN ). And if there are any non-numeric characters, you'll receive NaN .

See this question for more information.