I'm trying to create a textinput that only accepts numeric characters and the first character must be 3 in React Native.

            const [inputs, setInputs] = React.useState({
                num: '',
            });           

            let numOnly = /^[0-9\b] $/;
            let valid = true;
    
            if (!inputs.num.trim() || inputs.num.length < 10 || !inputs.num.match(numOnly)) {//if number field is not in correct format
                handleError('Please input phone number correctly', 'phone');
                valid = false;
            }

CodePudding user response：

Use this regex : /^3\d{9}$/

Description:

1. ^ assert position at start of the line
2. 3 first character must be 3.
3. \d{9} 9 characters after the first one has to be digits
4. $ assert position at the end of a line

As you specified the first character, the 9 next ones and start/end of the line, the total length has to be 10.

You can replace $ by \Z for end of the string instead of end of the line

CodePudding user response：

You can use below Regx to validate phone number:-

const reg = /^[0]?[3]\d{9}$/;
if (reg.test(phone) === true) {
  if (phone.length > 9) {
    console.log("valid phone number");
  } else {
    console.log("Invalid phone number");
  }
}

You can put the numbers in this array [3] like [3789] that you want to the phone number starts with.