use regex to test string match with only accept 1 and dot but 11 not acceptable

user_5605307 0
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I want to set a regex test to test the string is 1.1 or 1.1.1 or 1.1.1.1 etc but I only know this only accept 1 and .

/^[1\.]+$/.test(string)

If I test 1.11.1, it still return true.

javascript regex
4 Answers

If the string only accepts zero and one, but can not contain 11 you can use a negative look ahead to assert not 11.

Note that you don't have to escape the . in the character class.

^(?!.*11)[.1]+$

Regex demo

const regex = /^(?!.*11)[.1]+$/;
[
  "1.1",
  "1.1.1",
  "1.1.1.1",
  "...",
  "..1111",
  "1.1.....",
  "...1..1.."
].forEach(s => {
  const m = regex.test(s);
  if (m) {
    console.log(`Match -->  ${s}`);
  } else {
    console.log(`No match --> ${s}`);
  }
})

If there should be at least a . and a 1 present, you can add asserting a . and match at least a 1

^(?!.*11)(?=1*\.)[.]*1[.1]*$

Regex demo

const regex = /^(?!.*11)(?=1*\.)[.]*1[.1]*$/;
[
  "1.1",
  "1.1.1",
  "1.1.1.1",
  "...",
  "..1111",
  "1.1.....",
  "...1..1.."
].forEach(s => {
  const m = regex.test(s);
  if (m) {
    console.log(`Match -->  ${s}`);
  } else {
    console.log(`No match --> ${s}`);
  }
})

user_54249880

Try using ^1(?:\.1)*$:

var input = ["1", "1.1", "1.1.1.1", "1.2.3.4", "1.11", "hot dog"];
for (var i=0; i < input.length; i++) {
    if (/^1(?:\.1)*$/.test(input[i])) {
        result = "MATCH";
    }
    else { 
        result = "NO MATCH";
    }
    console.log(input[i] + " => " + result);
}

user_18632290

Try this

^(?:1\.)+[1]$|^(1)$

if you do not want to match 1 by itself

^(?:1\.)+[1]$
user_57376540

Another approach you might want to think about using here is to build a DFA. Since the regex is so simple, it does not take much effort:

function check(a){
  let isChecked = true;
  let STATE = 0;
    for(let i = 0; i < a.length; i++){
        if(STATE === 0 && a[i] === '1') STATE = 1;  
        else if(STATE === 1 && a[i] === '.') STATE = 0;
        else{ isChecked = false; }
    }
  if(STATE === 0) isChecked = false;
    return isChecked;
}

let arr = ['1', '1.11.1', '1.1.1.1', 'a.vad.bsadf.1', '1.1.111.1']
arr.forEach((a) => console.log(check(a)))

user_130677490
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