Welcome to Software Development on Codidact!

Will you help us build our independent community of developers helping developers? We're small and trying to grow. We welcome questions about all aspects of software development, from design to code to QA and more. Got questions? Got answers? Got code you'd like someone to review? Please join us.

Post History

57%

+2 −1

Q&A Function.prototype.call()

I wanted to print to browser console the number of li list items of a given ul list. This didn't work (console output was undefined): console.log(document.querySelectorAll(".example").length); ...

1 answer · posted 2y ago by deleted user · edited 2y ago by Alexei‭

Question javascript function prototype

#3: Post edited by

Alexei‭ · 2021-08-27T06:46:19Z (over 2 years ago)
added relevant tags

Copy Link

Raw

Markdown

javascript

javascript function prototype

#2: Post edited by (deleted user) · 2021-08-19T16:34:36Z (over 2 years ago)

Copy Link

Raw

Markdown

I wanted to print to browser console the number of `li` list items of a given `ul` list.
~~This didn't work (output was _undefined_):~~
```js
console.log(document.querySelectorAll(".example").length);
```
~~This worked (output was a plausible number):~~
```js
[].filter.call(
document.getElementsByClassName('example')[0].children,
function (el) {
return el.nodeName === 'LI';
}
).length
```
## My question
It was written in the [MDN page for Function.prototype.call()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/call):
> The call() method calls a function with a given this value and arguments provided individually.
But in the working code there was no "this".
What is the meaning of "call" in the second code?

I wanted to print to browser console the number of `li` list items of a given `ul` list.
This didn't work (console output was _undefined_):
```js
console.log(document.querySelectorAll(".example").length);
```
This worked (console output was a plausible number):
```js
[].filter.call(
document.getElementsByClassName('example')[0].children,
function (el) {
return el.nodeName === 'LI';
}
).length
```
## My question
It was written in the [MDN page for Function.prototype.call()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/call):
> The call() method calls a function with a given this value and arguments provided individually.
But in the working code there was no "this".
What is the meaning of "call" in the second code?

#1: Initial revision by (deleted user) · 2021-08-19T16:27:23Z (over 2 years ago)

Copy Link

Raw

Markdown

Function.prototype.call()

I wanted to print to browser console the number of `li` list items of a given `ul` list.

This didn't work (output was _undefined_):

```js
console.log(document.querySelectorAll(".example").length);
```

This worked (output was a plausible number):

```js
[].filter.call(
    document.getElementsByClassName('example')[0].children, 
    function (el) {
        return el.nodeName === 'LI';
    }
).length
```

## My question

It was written in the [MDN page for Function.prototype.call()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/call):

 > The call() method calls a function with a given this value and arguments provided individually.

But in the working code there was no "this".

What is the meaning of "call" in the second code?

javascript

Communities

Post History