Detect Pangram(js练习题codewars)

A pangram is a sentence that contains every single letter of the alphabet at least once. For example, the sentence "The quick brown fox jumps over the lazy dog" is a pangram, because it uses the letters A-Z at least once (case is irrelevant).

Given a string, detect whether or not it is a pangram. Return True if it is, False if not. Ignore numbers and punctuation.

function isPangram(string){
  let abc = 'abcdefghijklmnopqrstuvwxyz'
  let arr = abc.split('');
  str = string.toLowerCase()
  for(let c of str){
    let idx = arr.indexOf(c)
    if(idx > -1){
      arr.splice(idx,1)
    }
    
    if(arr.length == 0){
      return true
    }
  }
  return false
}