获得未定义但我想在 for 循环中使用 else 语句并显示“不存在”。 请帮我解决

Question

How can i use else statement in the following, would like to replace undefined to 'not exist', tried but not working. program: Check a given string contains 2 to 4 numbers of a specified character

 function check_char(x, y) { for (var j = 0; j < y.length; j++) { var d = y[j]; } for (var i = 1; i <= 3; i++) { data = x[i] console.log(data) if (data == d) { return d + " exist"; } } } document.write(check_char("Python", "y") + "<br>"); document.write(check_char("JavaScript", "a") + "<br>"); document.write(check_char("Console", "o") + "<br>"); document.write(check_char("Console", "C") + "<br>"); document.write(check_char("Console", "e") + "<br>"); document.write(check_char("JavaScript", "S") + "<br>");

**output:** 
y exist
a exist
o exist
undefined
undefined
undefined

Answer 1

Strictly speaking you don't need the else . Keep a count of the number of times the character appears in the string. If the count >= 2 and <= 4 return "exists" otherwise just return "does not exist".

You should avoid using document.write . This example has an extra function that creates some HTML using the string returned from the checkChar function, and then uses insertAdjacentHML to add it to the page.

 function checkChar(str, char) { // Initialise the count let count = 0; // Loop over the string - if the // letter in the iteration is the same as // the character increment the count for (const letter of str) { if (letter === char) ++count; } // If the count is within bounds return "exists" if (count >=2 && count <=4) { return `<span class="red">${char}</span> exists`; } // Otherwise return "does not exist" return `<span class="red">${char}</span> does not exist`; } function write(str) { // Create an HTML paragraph string with the string // returned from `checkChar`, and then add that // to the page const para = `<p>${str}</p>`; document.body.insertAdjacentHTML('beforeend', para); } write(checkChar('Python', 'y')); write(checkChar('JavaScript', 'a')); write(checkChar('Console', 'o')); write(checkChar('Console', 'C')); write(checkChar('Console', 'e')); write(checkChar('JavaScript', 'S'));

 .red { color: red; }

Answer 2

try this,

function check_char(x, y) {
  for (var j = 0; j < y.length; j++) {
    var d = y[j];
  }
  for (var i = 1; i <= 3; i++) {
    data = x[i]
    console.log(data)
    if (data == d) {
      return d + " exist";
    }
  }
  return 'not exist';
}