How to create a regex to delete letters and number after the 3rd decimal place

Question

I need a regular expression with the following rules:

• Erase all that is letter
• Delete all number after 3rd decimal place

For example, if I type 34,444 any next number will be deleted. If I type a will also be erased.

 $scope.validateLimits = function(){
    $scope.numLimiteInferior = $scope.numLimiteInferior.replace(/\d|,/g,'');
 }

Answer 1

The regex you used (/\d|,/) means "a digit or a comma", which means that you are replacing the numbers and commas with '' (that is, is removing all numbers and commas from the string).

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I suggest doing it in parts: first remove the letters and then remove the decimals:

let x = '3b4,4444444a';
x = x.replace(/[a-zA-Z]/g, '').replace(/(,\d{3})\d+/, '$1');
console.log(x); // 34,444

For letters I used [a-zA-Z] (any letter of a to z, uppercase or lower case).

To the decimal places I used parentheses to form a capture group, and within them I put ,\d{3} (comma followed 3 numbers). Since this part is within parentheses, if there is a comma followed by 3 numbers, they will be part of the capture group. And since it’s the first pair of parentheses, then it’ll be the first group.

Then there’s \d+ (one or more digits), and instead of substituting for the empty string, I use the reference $1, which means "everything that corresponds to the first capture group". In our case, it is the comma followed by 3 digits. Therefore, I keep the comma and the next 3 digits, and delete all numbers from the fourth decimal place onwards.

Also note that to remove the letters I use the flag g, for thus all letters are removed. Already in the second regex I do not use the g, 'cause I’m assuming there’s only gonna be one comma followed by numbers.

In addition, the regex /[a-zA-Z]/g does not consider accented letters. If you want, you can change it to /[a-záàâãéèêíïóôõöúçñ]/ig (with the option i to accept as many uppercase as lowercase, so it is shorter). If you want, in this question has other regex options for accented letters.