Implement condition in for..in loop

user_3916149 0
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I am looking at for..in tutorial from MDN documentation

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...in

The example iterates over the object's properties and prints all. I am trying to print only if value of object's property is 3. Can someone please help me understand where I am going wrong. And also if possible explain.

const object = { a: 1, b: 2, c: 3 };

for (const property in object.c == 3) {
  console.log(`${property}: ${object[property]}`);
}
for-in-loop javascript
4 Answers

for...in loops can't have conditions.¹ You have to implement the condition as an if within the loop:

for (const property in object) {
    if (object[property] === 3) {
        console.log(`${property}: ${object[property]}`);
    }
}

I've assumed you want any property with the value 3, not just c (since there'd be no need for a loop).

¹ "for...in loops can't have conditions" So why didn't you get an error? Because your code was syntactically correct, it just didn't do what you expected.

The for (const property in object.c == 3) is evaluated like this:

  1. Calculate the result of object.c == 3. Now we have:

    for (const property in true) // or `in false`

  2. Since for...in only works on objects, convert the boolean primitive to a Boolean object. Now we have:

    for (const property in new Boolean(true)) // or `in new Boolean(false)`

  3. Since Boolean objects have no enumerable properties, the loop never does anything.

user_1572470

You have to do every task step by step. The for in loop is for iteration. After that, you use an if conditional to check if the property is equals to 3. Check the code below:

const object = { a: 1, b: 2, c: 3 };

for (const property in object) {
    if(object[property]===3)
        console.log(`${property}: ${object[property]}`);
}
user_88820250

looks like you want to use for and if at same time.

You should try this:

const object = { a: 1, b: 2, c: 3 };

for (const property in object) {
    if(object[property]==3){
        console.log(`${property}: ${object[property]}`);
    }
}
user_173493590

for loop needs implementation of if condition bud, try this :



const object = { a: 1, b: 2, c: 3 };

for (const property in object) {
    if(object[property] == 3){
        console.log(`${property} : ${object[property]}`);
    }
}
user_197319090
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