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Accepted
Julian F
Asked: 2022-09-23 20:11:31 +0800 CST 2022-09-23 20:11:31 +0800 CST

How to validate a string using regular expressions and show the error in javascript?

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Today is the first time I touch the Java Script language. Since I was asked this: JS function must be created, which must receive a string . This entered string must meet the following conditions:

It should only contain alphanumeric characters. It must have a minimum length of 6 characters. It must start with an uppercase letter. It must have a maximum length of 12 characters.

However, being new to this language, I don't know if you can please advise me on the following code, since I feel that I am repeating several things. (the code in what I tested works)

    //let name_user = document.getElementById("campoUsuario").value;
    // se chequea el regex de que el string no tenga espacio
    var espacio = /\s/;
    //se chequea con el regex que no comience por números
    var numero_init = /^\d/ 
    //se chequea con el regex que solo tenga caracteres alfanumeros
    var char_alpha = /^[0-9a-zA-Z]+$/
    if(!espacio.test(name_user)){ 
        if(!numero_init.test(name_user)){
            if(char_alpha.test(name_user)){
                let longitud = name_user.length;
                if (longitud >=6 && longitud <= 8){
                    let letra = name_user.charAt(0)
                    if ( letra == letra.toUpperCase()){
                        return name_user;
                    }
                    else{
                        console.log("la primera letra no es mayuscula");
                        return false;
                    }    
                }
                else{
                    console.log("la longitud no cumple");
                    return false;
                }
            }
            else{
                console.log("no puede tener caracteres espciales");
                return false;
            }
        }
        else{
            console.log("El usuario no puede inciar con un número"); 
            return false;
        }
    }
    else{
        console.log("La contraseña no puede contener espacios en blanco"); 
        return false;
    }
}

let name_user = "San4566"
console.log(validar_usuario(name_user)); ```
javascript

1 Answers

  1. Best Answer

    You can base everything on a single regular expression

    function valida_usuario(name) {
    return /^[A-Z]\w{5,12}$/.test(name)
}

    Where:

    • ^[A-Z]indicate that the string must start with a capital letter
    • \w{5,12}consider strings of minimum length 5 and maximum 6, but each one is alphanumeric
    • \w{5,12}$must end with alphanumeric
    Note

    If you want to show specifically what fails you can use an array of conditions and just search if some condition is met or not.

    function valida_usuario(name) {
    const conditions = [
        { badPattern: /\W/, errorMessage: 'no puede tener caracteres espciales' },
        { badPattern: /\s/, errorMessage: 'La contraseña no puede contener espacios en blanco' },
        { badPattern: /^[^A-Z]/, errorMessage: 'El usuario no puede inciar con un número' },
        { badPattern: /^(\w{0,5}|\w{13,})$/, errorMessage: 'la longitud no cumple' },
    ]
    const badPattern = conditions.find(condition => condition.badPattern.test(name))

    if (badPattern) console.log(badPattern.errorMessage)

    return !badPattern
}
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