在“@”符号之前解析文本的电子邮件

Question

I'm trying to write a function that will take the email of the user as a parameter and return the first part of the email, up to but not including the "@" symbol. Problem is I'm terrible with functions, and there's something wrong with this function but I'm not sure what it is. When I try and write the function to the page to see if it worked correctly, it keeps showing up undefined.

function emailUsername(emailAddress)
{
    var userName = "";
    for(var index = 0; index < emailAddress.length; index++)
    {
        var CharCode = emailAddress.charCodeAt(index);
        if(CharCode = 64)
        {
            break;
        }
        else
        {
            userName += emailAddress.charAt(index);
            return userName;
        }
    }
}

var email = new String(prompt("Enter your email address: ",""));
var write = emailUsername(email);
document.write(write);

I'm sure there are other ways to do it but I need to follow roughly this format of using a function to check what's before the "@" and using methods to find it out.

Answer 1

像这样：

return emailAddress.substring(0, emailAddress.indexOf("@"));

Answer 2

function emailUsername(emailAddress) {
   return emailAddress.match(/^(.+)@/)[1];
}

Answer 3

Another possibility:

function emailUsername(emailAddress) {
  return emailAddress.split('@')[0]
}

This splits the string in half at the @ symbol, creating an array with the two parts and then retrieves the first item in the array, which will be the part before the @ .

Answer 4

If you want to be sure that it's an email (regex are not easy wiith real emails), you can use Masala Parser

import {C,Streams} from '@masala/parser'

function email() {

    const illegalCharSet1 = ' @\u00A0\n\t';
    const illegalCharSet2 = illegalCharSet1+'.';

    return C.charNotIn(illegalCharSet1).rep() // repeat( anyCharacter not illegal)
        .map(chars => ({start:chars.join()})) // will be kept by `.first()`
        .then(C.char('@'))
        .then(C.charNotIn(illegalCharSet2).rep())
        .then(C.char('.'))
        .then(C.charNotIn(illegalCharSet2).rep())
        .first(); // keep only the first  element of the tuple

}

let val = email().val('nicolas@masala.oss');
console.log(val); // {start:'nicolas')