Check if an Array Contains a Given Number

Question

Write a function to check if an array contains a particular number.

Examples check([1, 2, 3, 4, 5], 3) ➞ true

My code (i know that it can be done WAY EASIER)

function check(arr, el) {
 let sum = 0
 for (i= 0; i<= arr.length; i++) {
  if (arr[i]==el) {
   sum++; }
  else  
 }
 if (sum == 1) {
  return true;}
  else false;
}

Can you help me understand why this code does not work please?

Does this answer your question? [How do I check if an array includes a value in JavaScript?](https://stackoverflow.com/questions/237104/how-do-i-check-if-an-array-includes-a-value-in-javascript) — Garrett Motzner, Jun 04 '20 at 22:02
I spot a `}` right after `else` which is a syntax error. You can use your browser's development tools to see js errors. — lurker, Jun 04 '20 at 22:04
Your posted code has syntax errors and cannot execute at all. Pease fix the code so we can understand what is wrong with its logic. — Gabriele Petrioli, Jun 04 '20 at 22:07

Yosef Tukachinsky · Answer 1 · 2020-06-04T22:13:27.687

2

You have a built-in function for it - includes. Example usage:

[1,2,3,4].includes(3) // return true
[1,2,3,4].includes(8) // return false

Some of the other options:

some return true if the given condition return true for at least 1 of the array items, so you can do:
```
arr.some(item => item === value)
```

At the low level you can do:

for(let item of arr) if(item === value) return true;
return false;

edited Jun 04 '20 at 22:13

answered Jun 04 '20 at 22:05

Yosef Tukachinsky

5,570
1
13
29

score 0 · Answer 2 · answered Jun 04 '20 at 22:12

Your Code has an empty else clause.

function check(arr, el) {
    let sum = 0
    for (i= 0; i<= arr.length; i++) {
        if (arr[i]==el) {
            sum++; }
        else //<-- this else clause is empty and is causing you trouble 
    }
    if (sum == 1) {//This will only work if the element appears exactly once
        return true;}
        else false; //<-- and this won't return false as you intend.
}

Here is your code corrected.

function check(arr, el) {
let sum = 0
for (i= 0; i<= arr.length; i++) {
    if (arr[i]==el) {
        sum++; 
    }
}
if (sum >= 1) {
    return true;
}
return false;
}

And here is my example

function check(arr, el) {
    for(let i = 0; i < arr.length;i++){
        if(arr[i] === el){
            return true;
        }
    }
    return false;
}

Hope it is useful

score 0 · Answer 3 · answered Jun 04 '20 at 22:14

A couple of things.

Add a semicolon at the end of line 2. (This isn't necessarily necessary but prevents possible errors.)
Remove the equals from i<= arr.length in line 3 to assure that your not excessing an index of the array that doesn't exist.
You don't need the else in line 6. You have no code to run in the else statement so it isn't necessary.
At line 10, you have an else statement missing it's curling brackets. You need these around the code block you're running for the else statement. Also, you're missing the word return.

I've made a correct one here:

function check(arr, el) {
 let sum = 0;
 for (i = 0; i < arr.length; i++) {
  if (arr[i]==el) {
      sum++; 
        }  
 }
 if (sum == 1) {
        return true;
    } else {
        return false;
    }
}

score 0 · Answer 4 · answered Jun 04 '20 at 22:51

// Correction:
function check(array, element) {
  let itContains = false // Initialized to be boolean.

  for (let i = 0; i < array.length; i++) { // If you start with 0 you use '<' not '<='. Just count :)
    if (array[i] === element) { // Use '===' if you want to check if it is of the same type and value.
      itContains = true
      break // You do not need to go through the whole loop. You break it when you find a positive match.
    } // You do not need 'else' here because you initialized 'itContains' to be false.
  }

  return itContains // You just return proper boolean - false or true.
}

console.log(check([1, 2, 3, 4], 2)) // Returns 'true'.
console.log(check([1, 2, 3, 4], 5)) // Returns 'false'.

// Elegant solution:
function checkElegant(array, element) {
  return array.includes(element) // 'includes' method returns true or false.
}

console.log(checkElegant([1, 2, 3, 4], 2)) // Returns 'true'.
console.log(checkElegant([1, 2, 3, 4], 5)) // Returns 'false'.

Check if an Array Contains a Given Number

4 Answers4