Check if value exists in JavaScript array

Question

I have the following code snippet.

$scope.functionName = function(id) {
  var flag = true;
  var numbers = [1, 3, 30];

  for (var i = 0; i < numbers.length; i++) {
    if (id == numbers[i]) {
      flag = false;
    } else {
      flag = true;
    }
  }
  if (flag == true) {
    console.log("this is true");
  }
  if (flag == false) {
    console.log("this is true");
  }

}

What I want to perform is, if the input value is in the array, flag value should be false and if not it should be true. But, in this code snippet although flow goes inside the for loop after that it doesn't go to any of the if conditions. After entering the for loop it directly outputs "this is true". flag is always being true.

Why are you using "true" and "false" instead of true and false? — jonrsharpe
– jonrsharpe, Commented Apr 4, 2019 at 8:30
Thanks for pointing out that @jonrsharpe. Even though I changed flag to boolean still flow is not going inside comparing if condition. — Madhavee
– Madhavee, Commented Apr 4, 2019 at 8:34
try something shorter, like $scope.functionName = function(id){ return [1,3,30].includes(id)} — Vladimir Bogomolov
– Vladimir Bogomolov, Commented Apr 4, 2019 at 8:35

georgeawg · Accepted Answer · 2019-04-04 16:39:35Z

2

here is a cleaner approach at what you are trying to achieve

checkIfNumberIsInArray = function(number, arr) {
  return arr.includes(number)
}

console.log(checkIfNumberIsInArray(1, [1,2,3,4,5])) // true
console.log(checkIfNumberIsInArray(6, [1,2,3,4,5])) // false

See MDN JavaScript Reference - array.includes

edited Apr 4, 2019 at 16:39

georgeawg

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answered Apr 4, 2019 at 16:07

Lelouch

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Comments

Majedur · Accepted Answer · 2019-04-08 12:04:06Z

0

Add a break statement when your value equal to a value in array.

 $scope.functionName = function(id) {
      var flag = true;
      var numbers = [1, 3, 30];

      for (var i = 0; i < numbers.length; i++) {
        if (id == numbers[i]) {
          flag = false;
          break;
        } 
      }
      if (flag == true) {
        console.log("this is true");
      }
      if (flag == false) {
        console.log("this is false");
      }

    }

edited Apr 8, 2019 at 12:04

answered Apr 4, 2019 at 10:35

Majedur

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1 Comment

georgeawg Over a year ago

The else clause is a waste of time.

SkarXa · Accepted Answer · 2019-04-04 08:39:30Z

-1

You don't need to loop the array, just use indexOf. Also try to use number type for numbers, and boolean type for booleans, you are using string for both

$scope.functionName = function(id)
{
    var numbers = [1, 3, 30];

    var flag = numbers.indexOf(parseInt(id, 10)) > -1;  // Convert to number just in case

    if(flag === true)
    {
        console.log("this is true");
    }
    if(flag === false)
    {
        console.log("this is true");
    }
}

answered Apr 4, 2019 at 8:39

SkarXa

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