Check if a value is within a range of numbers

If you must use a regexp (and really, you shouldn't!) this will work:

/^0\.00([1-8]\d*|90*)$/

should work, i.e.

• ^ nothing before,
• followed by 0.00 (nb: backslash escape for the . character)
• followed by 1 through 8, and any number of additional digits
• or 9, followed by any number of zeroes
• $: followed by nothing else

Here is an option with only a single comparison.

// return true if in range, otherwise false
function inRange(x, min, max) {
    return ((x-min)*(x-max) <= 0);
}

console.log(inRange(5, 1, 10));     // true
console.log(inRange(-5, 1, 10));    // false
console.log(inRange(20, 1, 10));    // false

You're asking a question about numeric comparisons, so regular expressions really have nothing to do with the issue. You don't need "multiple if" statements to do it, either:

if (x >= 0.001 && x <= 0.009) {
  // something
}

You could write yourself a "between()" function:

function between(x, min, max) {
  return x >= min && x <= max;
}
// ...
if (between(x, 0.001, 0.009)) {
  // something
}