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I need to validate the first four digits in a phone number which should be "5678" in nodeJs how should I do it. Which validator library should I use

Amaan Imtiyaz
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    Stack Overflow expects you to [try to solve your own problem first](//stackoverflow.com/questions/261592/how-much-research-effort-is-expected-of-stack-overflow-users), as your attempts help us to better understand what you want. Please edit the question to show what you've tried, so as to illustrate a specific roadblock you're running into in [a minimal reproducible example](//stackoverflow.com/help/minimal-reproducible-example). For more information, please see [How to Ask](//stackoverflow.com/help/how-to-ask) and take the tour of the site. – Olaia Nov 08 '19 at 08:52
  • You don't need a library to do that, you can use a [regular expression](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions). – TGrif Nov 08 '19 at 10:00

2 Answers2

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It is best practice to depends on external library only if you need it, in my opinion.

In your case, you can check if your phone number start with "5678" with a very simple regular expression:

const validate_phone = /^5678/

var phone_number = '5678122535'
console.log(validate_phone.test(phone_number))  // true

var phone_number = '1567812253'
console.log(validate_phone.test(phone_number))  // false

^ stand for matches beginning of input

test stand for executes a search for a match between a regular expression and a specified string

TGrif
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You could use substring function which is better then regular expression in terms of complexity.

const string = "56789012345" ;
string.substring(0,4)==="5678" ? true : false ;
aaditya
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