Text Processing with JavaScript

Recipe 24

Asserting the Start or End of a String with ^ and $

Task

Suppose you have an input field in your app that allows customers to enter their order number and track their package. You want to ensure the user input is a number before searching it in your database. If you are a bit familiar with regex, you know that to match a digit with regex, you can use \d. And to match one or more digits, you can put a plus sign right after it like this:

part_2/caret_and_dollar/cnd_ex1.js

const input = "8751409";

function verifyDigits(input) {
  const re = /\d+/;
  return re.test(input);
}

verifyDigits(input);    // → true

This regex matches “8751409” as you intended. But it also matches a string like “123abc” or “abc123abc”:

part_2/caret_and_dollar/cnd_ex2.js ...