Check if a value is within a range of numbers

I want to check if a value is in an accepted range. If yes, to do something; otherwise, something else.

The range is 0.001-0.009. I know how to use multiple if to check this, but I want to know if there is any way to check it in a single if statement.

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
}

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

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

If you're already using lodash, you could use the inRange() function: https://lodash.com/docs/4.17.15#inRange

_.inRange(3, 2, 4);
// => true
 
_.inRange(4, 8);
// => true
 
_.inRange(4, 2);
// => false
 
_.inRange(2, 2);
// => false
 
_.inRange(1.2, 2);
// => true
 
_.inRange(5.2, 4);
// => false
 
_.inRange(-3, -2, -6);
// => true

I like Pointy's between function so I wrote a similar one that worked well for my scenario.

/**
 * Checks if an integer is within ±x another integer.
 * @param {int} op - The integer in question
 * @param {int} target - The integer to compare to
 * @param {int} range - the range ±
 */
function nearInt(op, target, range) {
	return op < target + range && op > target - range;
}

so if you wanted to see if x was within ±10 of y:

var x = 100;
var y = 115;
nearInt(x,y,10) = false

I'm using it for detecting a long-press on mobile:

//make sure they haven't moved too much during long press.
if (!nearInt(Last.x,Start.x,5) || !nearInt(Last.y, Start.y,5)) clearTimeout(t);

If you want your code to pick a specific range of digits, be sure to use the && operator instead of the ||.

if (x >= 4 && x <= 9) {
  // do something
} else {
  // do something else
}

// be sure not to do this

if (x >= 4 || x <= 9) {
  // do something
} else {
  // do something else
}

You must want to determine the lower and upper bound before writing the condition

function between(value,first,last) {

 let lower = Math.min(first,last) , upper = Math.max(first,last);
 return value >= lower &&  value <= upper ;

}

const inRange = (num, num1, num2) => Math.min(num1, num2) <= num && Math.max(num1, num2) >= num;

Could be like this if you want to make inRange inclusive and not depend on order of range numbers (num1, num2).