如何可靠地检查 Javascript 字符串是否为数字

Question

How do you determine if a string represents a number?

The straightforward and potentially naive way is this:

function is_number(my_str) {
  return !isNaN(parseInt(my_str));
}

However, the above does not work . Notice that the following all return true:

is_number("3, 4, 5");
is_number("3, (123)");
is_number("3, 123)");
is_number("3, (123) (and foo bar)");
is_number("3 apples and 2 oranges");

The issue is that parseInt seems to only look at the first word. Any idea on a more comprehensive solution here?

Answer 1

You can use Number() . parseInt and parseFloat converts String to Number if first character is a number. But Number() checks for whole String .Number return NaN if whole string is not number

 function is_number(my_str) { return !isNaN(Number(my_str)) && Boolean(my_str) || my_str == 0; } console.log(is_number("3, 4, 5")); console.log(is_number("3, (123)")); console.log(is_number("3, 123)")); console.log(is_number("3, (123) (and foo bar)")); console.log(is_number("3 apples and 2 oranges")); console.log(is_number(null)); console.log(is_number(undefined)); console.log(is_number(0)); console.log(is_number('0'));

Answer 2

All you need is Number

 console.log(Number("3, 4, 5") || false) console.log(Number("3, (123)") || false) console.log(Number("3, 123)") || false) console.log(Number('123') || false)

Answer 3

Here's my regular-expression based effort:

function isNumber (string) {
  return /^-?[0-9]+(?:\.[0-9]+)?(?:[eE][-+]?[0-9]+)?$/.test(string);
}

Includes support for leading sign, decimal places and exponent.

If it returns true , the string can be converted to a number using JSON.parse :

 function isNumber (string) { return /^-?[0-9]+(?:\\.[0-9]+)?(?:[eE][-+]?[0-9]+)?$/.test(string); } function convertNumber (string) { if (isNumber(string)) { return JSON.parse(string); } } [ '0', '1.2', '-3.4', '5.6789e100', '0.1e-100', '0.1e+100', ].forEach(string => { console.log(`isNumber('${string}'):`, isNumber(string)); console.log(`typeof convertNumber('${string}'):`, typeof convertNumber(string)); });