when i use this code i faced this problem, (Uncaught TypeError: Cannot read properties of undefined (reading 'startsWith'))

let friends = ["Ahmed", "Sayed", "Ali", 1, 2, "Mahmoud", "Amany"];
let index = 0;
let counter = 0;

// Output
"1 => Sayed"
"2 => Mahmoud"

while (index < friends.length) {
    index++
    if (typeof friends[index] === "number") {
        continue;
    }
    if (friends[index].startsWith(friends
0
+
网站访问量
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+
网站访问量
)) {
      continue;
    }
    console.log(friends[index])
}

And i Expect to get this output.

"1 => Sayed"
"2 => Mahmoud"

but console gave me this error Uncaught TypeError: Cannot read properties of undefined (reading 'startsWith')

Your problem is, that you increment the index at the start of the loop instead of at the end. This means, that when you are at index 6 it still satisfys the while condition and then in the loop gets incremented to 7 which is outofbounds for the friends Array. My solution would be to switch from a while loop to a for loop.

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

let friends = ["Ahmed", "Sayed", "Ali", 1, 2, "Mahmoud", "Amany"];
let counter = 0;

for (let index = 0; index < friends.length; index++) {
    if (typeof friends[index] === "number") {
        continue;
    }
    if (friends[index].startsWith(friends
0
+
网站访问量
0
+
网站访问量
)) {
      continue;
    }
    console.log(friends[index])
}

<!-- end snippet -->

Try adding friends[index] to your check. Also, your loop condition should be friends.length - 1

let friends = ["Ahmed", "Sayed", "Ali", 1, 2, "Mahmoud", "Amany"];
let index = 0;
let counter = 0;

while (index < friends.length -1) {
    index++
    if (typeof friends[index] === "number") {
        continue;
    }
    if (friends[index] && friends[index].startsWith(friends
0
+
网站访问量
0
+
网站访问量
)) {
      continue;
    }
    console.log(friends[index])
}