Question 244684 in Javascript Question posted in
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Javascript – 'undefined' output in console, using console.log()

I am new to JavaScript, try to learn how to read a function, it would be great if someone could look at this code and tell me why I am getting ‘undefined’ output here:

const myArray = [0, 1, 2, 3, 4, 5];

function arryIncludesMain(arr, item) {
  return arr.includes(item);
}

function arryIncludesAlt(arr, item) {
  if (arr.includes(item)) {
    console.log("true");
  } else {
    console.log("false");
  }
}

console.log(myArray.includes(8))

console.log("-----------------------------------------------");

console.log("Main function output:");
console.log(arryIncludesMain(myArray, 3));
console.log(arryIncludesMain(myArray, 6));
console.log("-----------------------------------------------");

console.log("Alt function output:");
console.log(arryIncludesAlt(myArray, 3));
console.log(arryIncludesAlt(myArray, 6));

And here is the console output:

false
-----------------------------------------------
Main function output:
true
false
-----------------------------------------------
Alt function output:
true
undefined
false
undefined

What is the difference between Main and Alt approach that I am getting ‘undefined’ output in console? what this ‘undefined’ refer to?

Tags:

3

Answers


  1. 0

    Functions return:

    In JavaScript, when a function does not have a return statement or when it reaches the end of the function without returning a value, it implicitly returns undefined.

    arryIncludesAlt() does not have a return statement, and instead, it uses console.log to print a string (true or false) to the console.

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  2. 0

    The reason you’re getting undefined, is because your arrayIncludesAlt function is not returning anything, instead it’s a ‘void’ method that logs
    the result. So you shouldn’t call console.log on this method.

    Instead of doing:

    console.log(arryIncludesAlt(myArray, 3)); // logs undefined
console.log(arryIncludesAlt(myArray, 6)); // logs undefined

    You should be doing:

    arryIncludesAlt(myArray, 3) // will do console.log while calling this function
arryIncludesAlt(myArray, 6) // will do console.log while calling this function

    As inside your arryIncludesAlt function you’re already logging the result.

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  3. 0

    The difference is "return" statement. It makes function to have a result.

    The alternate way is:

    function arryIncludesAlt(arr, item) {
  if (arr.includes(item)) {
    console.log("true");
  } else {
    console.log("false");
  }
  return arr.includes(item);
}
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