Regular expression begin in javascript

Question

I have an input text where user can write string. I want to have an regular expression in javascript which check if the string starts with three characters FSM. If the user write another string which doesn't start with FSM, this string was automatically remove and give the error message

Example:

FSMLERTE True
FSMAMAMA True
SFMABNE false et remove this content in the input

I do this but it's doesn't work

 var input22Regex= /^[a-z]$/;
 if(inputtxt.value.match(inputRegex)) {
 return true;
 } else {  
 inputtxt.value = '';
 alert("String must start with FSM");
 return false;

any idea ?

match returns an array with match information, see https://stackoverflow.com/questions/6603015/check-whether-a-string-matches-a-regex-in-js — Turo, Jun 24 '20 at 10:15

score 2 · Answer 1 · answered Jun 24 '20 at 10:16

Try the following:

const testRegex = /^FSM/;
function testString(str) {
  if (testRegex.test(str)) {
    return true;
  } else {
    console.log("String must start with FSM");
    return false;
  }
}

console.log(testString('FSMLERTE')); // true
console.log(testString('FSMAMAMA')); //true
console.log(testString('SFMABNE')); // false

score 1 · Answer 2 · answered Jun 24 '20 at 10:15

1

You can use startsWith

if(inputtxt.value.startsWith('FSM')) {
  return true;
} else {
  inputtxt.value = '';
  alert("String must start with FSM");
  return false;
}

answered Jun 24 '20 at 10:15

Salih Şenol Çakarcı

2,320
13
23

Hello @salih-Şenol-Çakarcı i want to use regular expression with check this, how can i do – obela06 Jun 24 '20 at 10:17
const regex = /^FSM/; regex.test(inputtxt.value) – Salih Şenol Çakarcı Jun 24 '20 at 10:19

score 0 · Answer 3 · answered Jun 24 '20 at 10:17

0

I think your regex should look like this

/^FSM(.)*/g

answered Jun 24 '20 at 10:17

kirsanv43

358
2
13

score 0 · Answer 4 · answered Jun 24 '20 at 10:23

You should use /^FSM[A-Z]*/ which will match all inputs that start with FSM and 0 or more capital letters following it. If you want it to be case-insensitive, you can use this instead: /^FSM[A-Z]*/i

var input22Regex = /^FSM[A-Z]*/;
if (inputtxt.value.match(inputRegex)) {
    return true;
} else {
    inputtxt.value = '';
    alert("String must start with FSM");
    return false;
}

score 0 · Answer 5 · edited Jun 24 '20 at 13:52

0

You can try this regex

FSM[a-zA-Z0-9]+

Demo

edited Jun 24 '20 at 13:52

Dharman

30,962
25
85
135

answered Jun 24 '20 at 10:25

Jay Parmar

368
2
9

It does not anchor to the start of string, so it will give unexpected matches for helloFSMxxx. Also it can't handle spaces, brackets, punctuation symbols, non ASCII symbols, arithmetic operation. – armagedescu Jun 24 '20 at 11:12

Regular expression begin in javascript

5 Answers5