How come I'm getting a numerical output instead of an array after using the array.push() method in this code?

In need of a custom function to append an element to the end of an array, I encountered a requirement: if this new element shares its value with any existing elements in the array, it should not be appended. For instance, adding 2 to [1,2] should result in [1,2] only.

This is the code snippet I came up with:

function add(arr, elem) {

    if (arr.indexOf(elem) != -1){
        return arr;
    }

    else {
        let newArr = arr.push(elem); 
        return newArr; 
    }

}

console.log(add([1,2],3)); // Expected output: [1,2,3], but received '3' instead

Can anyone shed light on why the 'newArr' array was not returned in the else block, and a number was returned instead?

javascriptarraysreturn-valuearray-push

Answer â„–1

When using Array.push, keep in mind that it does not return the entire array but rather the count of the new array.

Here is an example to demonstrate this:

const colors = ['red', 'blue', 'yellow'];
const count = colors.push('green');
console.log(count); // expected output: 4
console.log(colors); // expected output: Array ["red", "blue", "yellow", "green"]
  • If you are wondering about returning colors.push('green'), remember that it simply gives you the number of elements in the updated array after the push operation.

Answer â„–2

To display your current values, make sure to return the arr.

function addUniqueElement (arr, element){ 
      if (arr.indexOf(element) != -1){
           return arr;
      }
      arr.push(element); 
      return arr;
}

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