Negative match regex for positive and negative numbers with decimals

user_1046690 0
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I have regex expression which ensures that any characters which do not match the following criteria are replaced by an empty string:

  • Must be a number.
  • Optionally can be positive or negative.
  • Optionally can have decimal values, but not a trailing decimal point.

My problem: I am unable to figure out how to preserve the negative sign if it is found in front of the number. My regex currently replaces all instances of the '-' by an empty string. I am missing something here to ensure this issue does not occur.

var testId = document.getElementById('test');

var validate = value => {
  let regex = /([^\d.-]+)|([^\.?\d]+)/g;

  return value.toString().trim().replace(regex, '');
};

// Note: in comments, the expected output
var values = [
  '12345', // 12345
  '-12345', // -12345
  '12345.6789', // 12345.6789
  '-12345.6789', // -12345.6789
  '-123-45.-6789', // -12345.6789
  '$12345a6', // 123456
  '-1abcde+^~2345.6*#zZ789', // -12345.6789
  '50-00', // 5000
  '$12345' // 12345
];

values.forEach(value => {
  testId.innerHTML += `<p>${value} ==> ${validate(value)}</p>`;
});
<div id="test"></div>

ecmascript-6 javascript regex
1 Answers

You can use

return value.toString().trim().replace(/[^\d.-]+/g, '').replace(/^(-)|-/g, '$1');

Here,

  • .replace(/[^\d.-]+/g, '') - removes all chars other than digits, dots and hyphens
  • .replace(/^(-)|-/g, '$1') - only keeps the first hyphen in the string and removes all other hyphens. The point is that (-) captures the hyphen at the start (^ means the start of the string) into Group 1 that you can access with $1 backreference from the replacement pattern, and |- means "OR a hyphen that will be only matched in a non-initial position.

See the JavaScript demo:

var testId = document.getElementById('test');

var validate = value => {
  return value.toString().trim().replace(/[^\d.-]+/g, '').replace(/^(-)|-/g, '$1');
};

// Note: in comments, the expected output
var values = [
  '12345', // 12345
  '-12345', // -12345
  '12345.6789', // 12345.6789
  '-12345.6789', // -12345.6789
  '-123-45.-6789', // -12345.6789
  '$12345a6', // 123456
  '-1abcde+^~2345.6*#zZ789', // -12345.6789
  '50-00', // 5000
  '$12345' // 12345
];

values.forEach(value => {
  testId.innerHTML += `<p>${value} ==> ${validate(value)}</p>`;
});
<div id="test"></div>

user_38329700
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