How would this code be written without using the var keyword?

Question

1.00/5 (1 vote)

See more:

How would this code be written, and output the same result, if you used the let keyword rather than the var keyword

JavaScript

function constfuncs() {
    var funcs = [];
    for(var i = 0; i < 10; i++) 
       funcs[i] = function() { return i; };
    return funcs;
}

var funcs = constfuncs();
console.log(funcs[5]()); //Outputs 10

What I have tried:

I don't fully understand JavaScript hoisting, so I wanted to see how this piece of code would work when using a more understandable type of variable

Posted 9-May-18 12:51pm

Member 13814166

Updated 9-May-18 13:55pm

Add a Solution

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Dave Kreskowiak · Answer 1 · 2018-05-09T13:57:00

Solution 1

var declares a global variable while let declares a variable to a limited scope. In this case, the scope of the variable is inside the loop. Outside the loop, i doesn't exist.

If you leave this as var, the scope of the variable is the end constfuncs() function.

See this[^] for more information.

Posted 9-May-18 13:57pm

Dave Kreskowiak

Updated 9-May-18 14:03pm

v2

Comments

Member 13814166 9-May-18 20:13pm

I'm having trouble understanding how i in "function() { return i; };" is always 10. I thought only the declaration of i would be hoisted up, not the value it contained, am I incorrect in thinking this, or is there something I'm missing?

I would have assumed, if the output was the same, it would be written like this with lets rather than vars:

let i; //The declaration is hoisted up
function constfuncs() {
var funcs = [];
for(i = 0; i < 10; i++)
funcs[i] = function() { return i; };
return funcs;
}

var funcs = constfuncs();
console.log(funcs[5]()); //Outputs 5

Dave Kreskowiak 9-May-18 20:57pm

OK, this is different from what you asked above.

You're creating an array of functions, all of which are "return i;", NOT "return the current value of i at the time the function instance was created and put into the array.

At the end of the loop, the value of i is 10, so I'm not surprised every instance of the function returns 10.