Differentiate numbers and words in input using Regex

Question

I'm trying to create a simple program that will allow the user to input numbers or words and have them sorted alphabetically (in case of words) or numerically (in case of numbers). For this I need an input that will differentiate between numbers and words so that for example 10, -10, 0.5 and -0.5 will be evaluated as numbers and everything else will be considered words.

So far I have come up with this:

function recordUserInput() {
  userInput = $('input').val();

  if (userInput.charAt(0).match(/^(-)?[0-9]/)) {
    console.log('number', userInput);
  }
  else {
    console.log('text', userInput);
  }

}

However, negative numbers are still evaluated as text.

What am I doing wrong?

I really think Joseph's answer is the best approach rather than regex. However, the reason your regex didn't work was because you used `charAt(0).match` against your regex. In the case of negative numbers, `charAt(0)` is `-`, so it will never match against `^(-)?[0-9]`. You should have simply used `userInput.match` — Aserre, Nov 28 '16 at 13:42

Joseph · Accepted Answer · 2016-11-28T13:44:09.923

3

Use the unary +. If it returns NaN, it's not a number.

var type = isNaN(+userInput) ? 'text' : 'number';

parseFloat is probably not optimal. It parses left to right looking for a number and stops on a non-number. What it gathers, it turns to a number. parseFloat('123a') === 123.

edited Nov 28 '16 at 13:44

answered Nov 28 '16 at 13:36

Joseph

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And he needs to convert to number anyway to sort – mplungjan Nov 28 '16 at 13:39
1

Not need for `+`. `isNaN` works with strings as well. – georg Nov 28 '16 at 13:57

trincot · Answer 2 · 2016-11-28T14:23:58.157

Don't use .charAt(0) because you only look at the first character. Instead your regular expression is intended to look at the whole input, so just do (but add the + and $ at the end):

if (userInput.match(/^-?[0-9]+$/)) {

Once you have put the inputs in an array, you can sort it like this (which also demonstrates how to better test for numbers):

// Sample input:
var inputs = ['z', 1, 'a', 9, 3];

inputs.sort(function (a, b) {
    return isNaN(a) - isNaN(b) || isNaN(a) && a.localeCompare(b) || +a - +b;
});

console.log(inputs);

score 0 · Answer 3 · edited May 23 '17 at 12:30

You can write a small function isNumeric() to properly determine is a value is numeric. This is similar to the solution proposed in https://stackoverflow.com/a/9716488/1637175

function isNumeric(val) {
    return !isNaN(parseFloat(val)) && isFinite(val);
}

Your original function becomes

function recordUserInput() {
    userInput = $('input').val();

    if ( isNumeric(userInput) ) {
        console.log('number', userInput);
    }
    else {
        console.log('text', userInput);
    }
}

score 0 · Answer 4 · answered Nov 28 '16 at 13:52

0

If you want to check if an user input is a number or not, you can use something like this:

/^[-+]?\d+\.?\d*$/

it will match all number which might contain - or + at the beginning and dot symbol. Number like 10,-10.0 and +10.0 Example

answered Nov 28 '16 at 13:52

Anton Balaniuc

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Differentiate numbers and words in input using Regex

4 Answers4