老师，查到的是用toLowerCase()方法，但是在这里具体怎么使用呢。
/**

• @param {string} s

• @return {boolean}
  */
  var isNumber = function(s) {
  const graph = {
  0:{‘blank’:0, ‘sign’:1, ‘.’:2, ‘digit’:6},
  1:{‘digit’:6, ‘.’:2},
  2:{‘digit’:3},
  3:{‘digit’:3, ‘e’:4},
  4:{‘digit’:5, ‘sign’:7},
  5:{‘digit’:5},
  6:{‘digit’:6, ‘.’:3, ‘e’:4},
  7:{‘digit’:5}
  };

  let state = 0;
  for(c of s.trim()){
  if(c >= ‘0’ && c<=‘9’){
  c = ‘digit’;
  }else if(c === ’ ‘){
  c = ‘blank’;
  }else if(c===’+’ || c===’-’){
  c = ‘sign’;
  }
  state = graph[state][c];
  if(state === undefined){
  return false;
  }
  }
  if(state === 3 || state === 5 || state === 6){
  return true;
  }
  return false;
  };
  尝试了人家讲的几种方法，都报错了，求指导。