How to count list items in JavaScript?

Hi, I have the next list:

 
a
 
b
  

   
b1
   
b2
   
b3
  
 
 
c
 
d

I would like to know how can I count the LI elements from ‘myul’ ( just a,b,c,d )

But not count b1, b2 and b3, in this case the function should return 4

Thanks

We can access the length property on the filtered array to get the count of the elements that meet the condition.

You can also shorten the function by returning the comparison instead of returning true or false.

We directly check if each element is greater than 10 and return the result instead of explicitly returning true and false.

An alternative approach is to use the Array.reduce method.

Count Elements in an Array that match a Condition using length1

To count the elements in an array that match a condition:

1. Use the length1 method to iterate over the array.
2. If the element matches the condition return the length3 value + 1.
3. If the condition is not matched, return the length3.

The function we passed to the Array.reduce method gets called for each element in the array.

We initialized the length3 variable to a length6 because that's what we passed as the second argument to the length1 method.

On each iteration, we check if the current element is greater than 10.

If the condition is met, we return the length3 value + 1, otherwise, we return the length3.

The value we return from the callback function gets passed as the length3 for the next iteration.

After the last iteration, the filter()2 method returns the count of the array elements that match the condition.

Count Elements in an Array that match a Condition using filter()3

To count the elements in an array that match a condition:

1. Declare a filter()4 variable and initialize it to length6.
2. Use the filter()6 method to iterate over the array.
3. Check if each element meets the condition.
4. Increment the filter()4 variable if the condition is met.

The function we passed to the Array.forEach method gets called with each element in the array.

The filter()3 method returns filter()9, so we have to perform some kind of mutation to persist the state.

On each iteration, we check if the current array element is greater than 10.

If the condition is met, we increment the filter()4 variable by 102.

Notice that we used 103 to declare the filter()4 variable. Variables declared using 105 cannot be reassigned.

Count Elements in an Array that match a Condition using 106

You can also use a 106 loop to count the elements that match a condition.

The for...of statement is used to loop over iterable objects like arrays, strings, 108, 109 and true0 objects and true1.

On each iteration, we check if the current element meets the condition and if it does, we increment the filter()4 variable by 102.

Count Elements in an Array that match a Condition using a true4 loop

You can also use a basic true4 loop to count the elements in an array that meet a condition.

The true4 loop is quite verbose and requires us to make use of the index to access the current array element.

Which approach you pick is a matter of personal preference. I'd use the filter()6 method because I find it more direct.

Knowing how to quickly iterate through an array and count objects is deceptively simple. The

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

let counter = 0;
for (let i = 0; i < storage.length; i++) {
  if (storage[i].status === '0') counter++;
}

console.log(counter); // 6

For example, imagine you have an array like this:

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

And you only want to count the number of objects with

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

let counter = 0;
for (let i = 0; i < storage.length; i++) {
  if (storage[i].status === '0') counter++;
}

console.log(counter); // 6

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

let counter = 0;
for (let i = 0; i < storage.length; i++) {
  if (storage[i].status === '0') counter++;
}

console.log(counter); // 6

Like with just about everything in programming, there are a number of ways to do this. We'll go through a few of the common methods below.

Use a const storage = [ { data: '1', status: '0' }, { data: '2', status: '0' }, { data: '3', status: '0' }, { data: '4', status: '0' }, { data: '5', status: '0' }, { data: '6', status: '0' }, { data: '7', status: '1' }, ]; let counter = 0; for (let i = 0; i < storage.length; i++) { if (storage[i].status === '0') counter++; } console.log(counter); // 63 loop

Probably the easiest way would be to declare a

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

let counter = 0;
for (let i = 0; i < storage.length; i++) {
  if (storage[i].status === '0') counter++;
}

console.log(counter); // 6

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

let counter = 0;
for (let i = 0; i < storage.length; i++) {
  if (storage[i].status === '0') counter++;
}

console.log(counter); // 6

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

let counter = 0;
for (let i = 0; i < storage.length; i++) {
  if (storage[i].status === '0') counter++;
}

console.log(counter); // 6

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

let counter = 0;
for (let i = 0; i < storage.length; i++) {
  if (storage[i].status === '0') counter++;
}

console.log(counter); // 6

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

let counter = 0;
for (let i = 0; i < storage.length; i++) {
  if (storage[i].status === '0') counter++;
}

console.log(counter); // 6

You could simplify this a bit by using a

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

let counter = 0;
for (let i = 0; i < storage.length; i++) {
  if (storage[i].status === '0') counter++;
}

console.log(counter); // 6

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

let counter = 0;
for (const obj of storage) {
  if (obj.status === '0') counter++;
}

console.log(counter); // 6

Also, you could create a function to do the same thing if you have other arrays of objects to count conditionally:

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

function statusCounter(inputs) {
  let counter = 0;
  for (const input of inputs) {
    if (input.status === '0') counter += 1;
  }
  return counter;
}

statusCounter(storage); // 6

Use array methods

JavaScript includes a bunch of helpful methods when working with arrays. Each one can be chained to an array and passed different parameters to work with while iterating through the elements in the array.

The two we'll look at are

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

let counter = 0;
for (let i = 0; i < storage.length; i++) {
  if (storage[i].status === '0') counter++;
}

console.log(counter); // 6

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

let counter = 0;
for (const obj of storage) {
  if (obj.status === '0') counter++;
}

console.log(counter); // 6

const storage = [ { data: '1', status: '0' }, { data: '2', status: '0' }, { data: '3', status: '0' }, { data: '4', status: '0' }, { data: '5', status: '0' }, { data: '6', status: '0' }, { data: '7', status: '1' }, ]; let counter = 0; for (let i = 0; i < storage.length; i++) { if (storage[i].status === '0') counter++; } console.log(counter); // 69

The filter method does just that – it iterates through each element in the array and filters out all elements that don't meet the condition(s) you provide. It then returns a new array with all the elements that returned true based on your condition(s).

For example:

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

const count = storage.filter(function(item){
  if (item.status === 0) {
    return true;
  } else {
    return false;
  }
});

/*
[
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' }
] 
*/

Now that you've filtered out the object with

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

let counter = 0;
for (const obj of storage) {
  if (obj.status === '0') counter++;
}

console.log(counter); // 6

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

let counter = 0;
for (let i = 0; i < storage.length; i++) {
  if (storage[i].status === '0') counter++;
}

console.log(counter); // 6

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

let counter = 0;
for (const obj of storage) {
  if (obj.status === '0') counter++;
}

console.log(counter); // 6

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

const count = storage.filter(function(item){
  if (item.status === 0) {
    return true;
  } else {
    return false;
  }
}).length; // 6

But this can be shortened a lot with ES6 syntax:

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

const count = storage.filter(item => item.status === '0').length; // 6

const storage = [ { data: '1', status: '0' }, { data: '2', status: '0' }, { data: '3', status: '0' }, { data: '4', status: '0' }, { data: '5', status: '0' }, { data: '6', status: '0' }, { data: '7', status: '1' }, ]; let counter = 0; for (const obj of storage) { if (obj.status === '0') counter++; } console.log(counter); // 60

Think of the

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

let counter = 0;
for (const obj of storage) {
  if (obj.status === '0') counter++;
}

console.log(counter); // 6

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

let counter = 0;
for (let i = 0; i < storage.length; i++) {
  if (storage[i].status === '0') counter++;
}

console.log(counter); // 6

You can read more about

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

let counter = 0;
for (const obj of storage) {
  if (obj.status === '0') counter++;
}

console.log(counter); // 6

For our purposes, we want to take an array, examine its contents, and produce a number. Here's a simple way to do that:

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

const count = storage.reduce((counter, obj) => {
  if (obj.status === '0') counter += 1
  return counter;
}, 0); // 6

You could simplify further by using ES6 syntax and a ternary operator:

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

const count = storage.reduce((counter, obj) => obj.status === '0' ? counter += 1 : counter, 0); // 6

And even a bit more by using object destructuring:

const storage = [
  { data: '1', status: '0' },
  { data: '2', status: '0' },
  { data: '3', status: '0' },
  { data: '4', status: '0' },
  { data: '5', status: '0' },
  { data: '6', status: '0' },
  { data: '7', status: '1' },
];

const count = storage.reduce((counter, { status }) => status === '0' ? counter += 1 : counter, 0); // 6

So those are a few ways to go through the elements of an array and count them conditionally. Now get out there and count with confidence!

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