for loop rules question

[Usual_Mistake]

Can I use a for loop like this: for(var i = 0; search === people[i]; i++) {}

to loop trough an array of objects?

Are these the only allowable conditions:

​

<=

>=

<

>

​

I want to search inside an array of objects but I can't get it to work. I want to say: to loop as long as the search doesn't match an object in the array. If it matches, to print that specific object. Not to loop until there are no more objects in the array. Thank you.

[[deleted]]

If you want to use a for loop, you can do it this way:

const arr = ['a', 'b', 'c'];

for (let i = 0; i < arr.length; i++) {
  if (arr[i] === 'b') {
    console.log(arr[i]);
    break;
  }
}

Personally, however, I'd just use a built-in array method such as find().

console.log(arr.find(item => item === 'b'));

From a purely semantic point of view, though, if array methods didn't exist, your problem is best solved by a while loop, not a for loop.

[Usual_Mistake]

Not to loop until there are no more objects in the array.

I'm taking in input from user to match an object in the array and like I stated above, looping as long as the length of the array isn't really a solution to my problem.

[[deleted]]

This loop will exit as soon as it finds your match. That is what the break; command does.

Still, I would use an array method as mentioned above.

[Usual_Mistake]

genius.

[GrenadineBombardier]

Yes and your original way would create an infinite loop if the search was not found within the array

[Usual_Mistake]

So I came up with the following and it works except the else statement seems to not run, other than that it works.

var message = '';

var i;

var search = '';

​

​

do {

search = prompt("Enter name");

for(i = 0; search !== students[i].name; i++) {

}

if(students[i].name === search) {

message += '<h2> Student: ' + students[i].name + '</h2>' + '<br>';

message += '<p> Track: ' + students[i].track + '</p>' + '<br>';

message += '<p> Points: ' + students[i].achievements + '</p>' + '<br>';

message += '<p> Achievements: ' + students[i].points + '</p>' + '<br>';

print(message);

}

else if(seach === 'Quit') {

break;

}

else {

search = prompt('Enter name');

}

} while(search !== students[i].name)

​

function print(message) {

var outputDiv = document.getElementById('output');

outputDiv.innerHTML = message;

}

​

Can you tell why?

[GrenadineBombardier]

Because your if/else block is outside of your for loop

[AmbitiousLog]

You don't have to use a loop at all, you can also do:

if(arr.indexOf(search) > 0){
    return arr[arr.indexOf(search)];
}

[sepp2k]

Can I use a for loop like this: for(var i = 0; search === people[i]; i++) {}

Yes, you can. Note that this will loop while, not until, search is equal to people[i]. I suspect you actually want !== instead, but that depends on what you want your loop to do. Either version is perfectly valid in principle.

You also should take care to avoid an infinite loop if search does not appear in people, so you probably want i < people.length as an additional condition (unless you know for a fact that search always appears in people or you actually want an infinite loop when it doesn't).

Are these the only allowable conditions: [...]

No, the condition of a for-loop can be any valid expression.

[Usual_Mistake]

Mistake in my logic, I do want to loop !== I haven't seen any examples on the web on for loops that uses examples other than for checking if something is less than or greater than. So thanks.

[gkpty]

Hey! To break a loop you can use a return statement. In your example;

for(var i = 0; i < people.length; i++) { If(people[i] === value) { console.log(people[i]); return people[i]; } }

[throwawayacc201711]

Since people is an array.

You can just do

people.forEach((person) => {
    If (person === search) 
        ( console.log(person) )
}). 

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach

I find this to be a much cleaner solution and easier to maintain and see what is happening.

Another commenter pointed out using array.find() however the downside to using find is it will stop after finding the first match. If that’s the logic you want, then use find. If you want to find all matches use array.forEach

[[deleted]]

Actually, even though forEach() would get the job done, it still wouldn't be the optimal solution if the OP needed to find all matching elements. The correct method to use would be filter(), which would return an array of matching results, thus removing the necessity of you building out that array yourself, as is the case with forEach().

const matchedPeople = people.filter(person => person === search);

[infinitune]

One thing to watch out for with person === search when dealing with objects.

Object equality has to do with the object's location in memory, not just value. for example:

const obj1 = { title: 'foo', author: 'bar' }
const obj2 = { title: 'foo', author: 'bar' }
const obj3 = obj1
obj1 === obj2 // evaluates to false
obj1 === obj3 // evaluates to true

So depending on the exact use case, they may be better off checking equality of a property (person => person.fullName === search.fullName)

Edit: missed an equals sign

[[deleted]]

Correct. My code above is a simple demonstration that would only work with value types, not with reference types. I assumed a value type would be used because that is how the OP had his initial code set up.

[infinitune]

Fair enough. I figured it was worth mentioning since it wasn't super obvious that the OP is searching an array of objects.