Simple Symbols code challenge

/**
 *           
This challenge requires you to determine if every alphabetic character in a string has a plus (+) symbol on the left and right side of itself. For example: the string "+a+b+c+" is good but the string "===+3+f=+b+" is not because the "f" does not have a plus symbol to its right. A very simple way to solve this challenge is to create a loop that every time it gets to an alphabetic character, it checks to see if it is surrounded by + symbols.
 */

/* Not pure f */
function SimpleSymbols(str) {
  var str = "=" + str + "=";

  for (var i = 0; i < str.length; i++) {
    if (str[i].match(/[a-z]/i) !== null) {
      // -1 to begging and + 1 to end
      if (str[i - 1] !== "+" || str[i + 1] !== "+") {
        return false;
      }
    }
  }

  return true;
}

/* Else If & Regex test() */
function SimpleSymbols2(str) {
  if (/^[a-zA-Z]/.test(str) || /[a-zA-Z]$/.test(str)) {
    return false;
  } else if (/[^+][a-zA-Z]/.test(str) || /[a-zA-Z][^+]/.test(str)) {
    return false;
  } else {
    return true;
  }
}

/* heavy comparing conditional  */
function SimpleSymbols(str) {
  let answer = "true";
  let string = "=" + str + "=";
  for (let i = 1; i < string.length - 1; i++) {
    if (
      string[i].match(/[a-z]/i) !== null &&
      (string[i - 1] !== "+" || string[i + 1] !== "+")
    ) {
      answer = "false";
    }
  }
  return answer;
}

/* Split */
function SimpleSymbols(str) {
  var ref;
  if (str.match(/\+\w\+/g) === null) {
    return false;
  } else {
    ref = str
      .split("")
      .map(function(e, i, arr) {
        if (/[a-z]/g.test(e)) {
          return arr[i - 1] === "+" && arr[i + 1] === "+" ? "o" : "x";
        } else {
          return "x";
        }
      })
      .join("");
    return ref.match(/o/g).length === str.match(/[a-z]/g).length;
  }
}

/* subtstrings */
function SimpleSymbols(str) { 
  if(str.charAt(0).match(/[a-z]/i)) return false;
  if(str.charAt(str.length-1).match(/[a-z]/i)) return false;
for (j=1;j<str.length;j++){
  if(str.charAt(j).match(/[a-z]/i) && (str.substr(j-1,1) != "+" || str.substr(j+1,1) != "+") )
      return false;
  }
  return true;
}
  
SimpleSymbols(readline());