Return true if the string in the first element of the array contains all of the letters of the string in the second element of the array.
For example, ["hello", "Hello"], should return true because all of the letters in the second string are present in the first, ignoring case.
The arguments ["hello", "hey"] should return false because the string "hello" does not contain a "y".
Lastly, ["Alien", "line"], should return true because all of the letters in "line" are present in "Alien".
TEST☟
mutation(["hello", "hey"]) should return false.
mutation(["hello", "Hello"]) should return true.
mutation(["zyxwvutsrqponmlkjihgfedcba", "qrstu"]) should return true.
mutation(["Mary", "Army"]) should return true.
mutation(["Mary", "Aarmy"]) should return true.
mutation(["Alien", "line"]) should return true.
mutation(["floor", "for"]) should return true.
mutation(["hello", "neo"]) should return false.
mutation(["voodoo", "no"]) should return false.

//wrong.  arr[0].toLowerCase().indexOf(arr[1].toLowerCase())!==-1只能判断arr[1].toLowerCase()整个字符是否在arr[0].toLowerCase()中
function mutation(arr) {
  if(arr[0].toLowerCase().indexOf(arr[1].toLowerCase())!==-1){
    return ture;
  }else {
    return false;
  }  
}
mutation(["hello", "hey"]);```

//有问题？？
//return false; 位置问题，需要放在for循环后才符合逻辑
function mutation(arr) {
var target = arr[0].toLowerCase();
var test = arr[1].toLowerCase();
for (var i = 0; i < test.length; i++) {
if (target.indexOf(test[i])!==-1) {
return true;
}
return false;
}
}
mutation(["hello", "hey"]);//true```

function mutation(arr) {
  var test = arr[1].toLowerCase();
  var target = arr[0].toLowerCase();
  for (var i=0;i<test.length;i++) {
    if (target.indexOf(test[i]) < 0){
      return false;
    }    
  }
  return true; 
}
mutation(["hello", "hey"]);```

copy from https://github.com/freeCodeCamp/freeCodeCamp/wiki/Algorithm-Mutations