将Python代码实现为Javascript时，我在做什么错？

Question

I have the next python code:

letter = ['a', 'b', 'c', 'd']
word = "Black"
for i in word:
    if i in letter:
        print(i)

So, I'm trying to do the same in JS :

var letter = ['a', 'b', 'c', 'd'];
var word = "Black";
var dictionary = [];
var dictionaryCoincidence = [];

for (var i = 0; i < word.length; i++) {
    dictionary.push(word[i]);
}

for (var i = 0; i < dictionary.length; i++) {
    if (dictionary[i] == letter[i]) {
        dictionaryCoincidence.push(dictionary[i]);
    }
}

console.log(dictionary);
console.log(dictionaryCoincidence);

But, it doesn't work!

Answer 1

You can use Array.includes() to check if some element belongs to an array, then use a for ... of loop to traverse the string and do something like this:

 const letter = ['a', 'b', 'c', 'd']; const word = "Black"; for (const char of word) { if (letter.includes(char)) console.log(char); } 

 .as-console {background-color:black !important; color:lime;} .as-console-wrapper {max-height:100% !important; top:0;} 

Answer 2

In the spirit of functional python I suggest using filter since it works like the filter in python. The question is on both Python and Javascript so :)

 var letter = ['a', 'b', 'c', 'd']; var word = "Black"; var filtered = word.split("").filter(x => letter.includes(x)) console.log(filtered) 

Answer 3

You don't really need second for loop.. Just check the word[i] is in the letter array or not, and you can do it by using "includes" or "indexOf"..

 var letter = ['a', 'b', 'c', 'd']; var word = "Black"; var dictionary = []; var dictionaryCoincidence = []; for (var i = 0; i < word.length; i++) { dictionary.push(word[i]); if (letter.includes(word[i])) { dictionaryCoincidence.push(dictionary[i]); } } console.log(dictionary); console.log(dictionaryCoincidence); 

Answer 4

You must use two loop : one loop for dictionary and one loop for letters like this:

    var letter = ['a', 'b', 'c', 'd'];
    var word = "Blackd";
    var dictionary = [];
    var dictionaryCoincidence = [];

   for (var i = 0; i < word.length; i++) {
    dictionary.push(word[i]);
   }

   for (var i = 0; i < dictionary.length; i++) {
       for(var j = 0; j < letter.length ; j++){
           if (dictionary[i] == letter[j]) {
             dictionaryCoincidence.push(dictionary[i]);
           }
        }
   }

   console.log(dictionary);
   console.log(dictionaryCoincidence);

Answer 5

Try changing the second loop to

for (var i = 0; i < dictionary.length; i++) {
    if (letter.includes(dictionary[i])) {
        dictionaryCoincidence.push(dictionary[i]);
    }
}

You need to check that the dictionary[i] is in the letter array, and not that it equals to letter[i]

1. It gives you the result [a,c] . B is not included, because it's uppercase. Cast dictionary[i] to lowercase if you need the letter B to.
2. You can use letter.indexOf method instead of includes(). So condition letter.indexOf(dictionary[i])>-1 also works