CODEWITHSUNDEEP
javascript
Mahesh G
Mahesh G

Reputation: 1276

Comparision is not working in Javascript with Strict Equal

I have below Basic Javascript to reverse the number which work when I use

while (!no == 0)

But Doesn't work when I use

while (!no === 0)

I have tried in the console for parseInt(0) which returns number only and my no is already number so

why === is not working ,Can someone help and explain me better?

function findRepeated(number) {
  var a, no, b, temp = 0;

  no = parseInt(number);


  while (!no == 0) {
    a = no % 10;
    no = parseInt(no / 10);
    temp = temp * 10 + a;
  }
  return temp;
}

console.log(findRepeated(123));

Upvotes: 5

Views: 370

Answers (2)

JO3-W3B-D3V
JO3-W3B-D3V

Reputation: 2134

Types

!no returns a boolean, it returns false, although the value of no is a number, adding the negate operator in front of any number will return a false, i.e. console.log(!123 === false). As you're probably aware, using == will convert the data type for you, where as using === will not.

Example

I like the example of null and undefined. While null == undefined is true, null === undefined is false, because the value null is a type of object, whereas the type of undefined is of course undefined.

console.log("test1: " + !123); // false
console.log("test2: " + (!123 === false)); // true
console.log("test3: " + (!123 == 0)); // true
console.log("test4: " + (!123 === 0)); // false

console.log("test5: " + (0 == false)); // true
console.log("test6: " + (0 === false)); // false
console.log("test7: " + (null == undefined)); // true
console.log("test8: " + (null === undefined)); // false

console.log("test9: " + typeof null); // object
console.log("test10: " + typeof undefined); // undefined

Upvotes: 4

axiac
axiac

Reputation: 72256

!no == 0 is not the same as !(no == 0). It is (!n) == 0.

Similar, !no === 0 is (!no) === 0.
This always evaluates to false because !no is a boolean and 0 is a number.
Values of different types are never ===.

Read about the logical NOT operator, the comparison operators and operator precedence.

Upvotes: 8

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