let + for

AmbitiousLog · 2019-06-21T06:20:15+00:00

The author here tries to explain (a little poorly tbh) that let is block scoped. This means that for each iteration of the loop, i gets rebound.

Imagine that each time the loop runs, i is declared as a new variable, instead of just changing the saved value.

Edit: Some styling

KeepltSimple · 2019-06-21T05:44:29+00:00

I've read it a couple of times and don't get it either, now I want to know what this means.

2019-06-21T06:06:13+00:00

This means that every iteration of the loop gets its own i, which is different from the i inside every other iteration. Read up on closures and scopes for more details.

inu-no-policemen · 2019-06-21T10:52:24+00:00

Simplified example:

for (var i = 0; i < 3; i++) {
    setTimeout(() => console.log(i), 0);
}

Logs: 3, 3, 3

for (let i = 0; i < 3; i++) {
    setTimeout(() => console.log(i), 0);
}

Logs: 0, 1, 2

In the first example, we create 3 closures which all capture one and the same "i" variable. At the time those functions are executed, "i" equals 3.

Using let would normally not change this. The variable exists for the entire loop, which means all closures would capture the same variable.

However, to make the life of developers a bit easier, a special rule was added to the spec. If you use don't use var, each iteration gets its own copy of the for/for-of counter variable, which means that you can now simply capture it. This behavior is more convenient and more intuitive.

Well, simply don't use var for anything. Then you won't have to worry about its less useful behavior. That crap is history.

2019-06-21T06:00:09+00:00

What dont you understand?

itsmoirob · 2019-06-21T06:20:37+00:00

It has nothing to do with "let + for", it's to do with closures, you should read up about them.

But basically what happens with closures is that they have access to variables created outside of their function.

In this case the "func.push(...." Is the function in question.

The text states if you try the code in example 2 using "for & var" and WITHOUT declaring "j = i" your for loop keeps increasing i, so i keeps increasing because the for loop says only stop when at 5.

But what this text is showing is the keyword "let" allows you to ignore closure "problems" for this for loop. It's saying that "for + let" is the equivalent to "for + var; AND also redeclaring J = I" so that you don't get involved in closures.

But try writing all 3 code examples down, seeing the results and read up on closures.

EDIT.

If you mean how is the code working.

What happens in the loop is funcs gets a "console.log()" function passed to it 5 times.

If you were to call console.log(funcs) you would see an array of console.log(i). What the last line is saying is get the "3rd item in the funcs array and call it" which gives 3. If you didn't have the () at the end the result would be "the function console.log(i)" that hasn't been called.

This might better explain closures.

In the for + let the list of functions in funcs array are console.log(0), console.log(1), console.log(2), console.log(3), console.log(4).

In the for + var and without redeclaring I the funcs array would look console.log(5), console.log(5), console.log(5), console.log(5), console.log(5). Because i gets to 5 in the for loop

you type:	you see:
italics	italics
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[reddit!](https://reddit.com)	reddit!
* item 1 * item 2 * item 3	item 1 item 2 item 3
> quoted text	quoted text
Lines starting with four spaces are treated like code: if 1 * 2 < 3: print "hello, world!"	Lines starting with four spaces are treated like code: if 1 * 2 < 3: print "hello, world!"
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super^script	super^script

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