JavaScript回文数

　基本解决方案

function palindrome(str) {
  return str.replace(/[W_]/g, '').toLowerCase() ===
         str.replace(/[W_]/g, '').toLowerCase().split('').reverse().join('');
}

中间代码解决方案

function palindrome(str) {
  str = str.toLowerCase().replace(/[W_]/g, '');
  for(var i = 0, len = str.length - 1; i < len/2; i++) {
    if(str[i] !== str[len-i]) {
      return false;
    }
  }
  return true;
}

 高级代码解决方案（性能最高）

function palindrome(str) {

  let front = 0;
  let back = str.length - 1;

  //back and front pointers won't always meet in the middle, so use (back > front)
  while (back > front) {
    //increments front pointer if current character doesn't meet criteria
    while ( str[front].match(/[W_]/) ) {
      front++;
      continue;
    }
    //decrements back pointer if current character doesn't meet criteria
    while ( str[back].match(/[W_]/) ) {
      back--;
      continue;
    }
    //finally does the comparison on the current character
    if ( str[front].toLowerCase() !== str[back].toLowerCase() ) return false
    front++;
    back--;
  }
  
  //if the whole string has been compared without returning false, it's a palindrome!
  return true;

}