["dwdwad","dwdawd","dwdwad","ddd","sss"]，找“ddd”这个字符串的索引，怎么样牺牲空间复杂度，换取时间复杂度为O(1)

gistfile1.txt

var i, arr = ["dwdwad","dwdawd","dwdwad","ddd","sss"], target = 'ddd';

var hash = {};

for(i = 0; i < arr.length; ++i) {
  hash[arr[i]] = i;
}
console.log(hash[target]);