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

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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

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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

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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.

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

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

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