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Comments on Uncaught ReferenceError: variable is not defined

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Uncaught ReferenceError: variable is not defined

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I have a variable defined using const keyword.

function Text() {
    const variable = "Hello!";
}

console.log(variable);

When I try to access this variable, I get:

Uncaught ReferenceError: variable is not defined

What am I missing?

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const is block-scoped. Which means that const can be only accessed inside the block-scope that it were declared in. Block-scope means code enclosed by Curly braces {}. Functions are also blocks.

If you really want to use const, so the solution is to define the variable outside the block-scope (In other words, outside the function).

Here is an example:

const variable = "Hello!";

function Text() {
    console.log(variable); // Hello - Inside the block scope
}

Text(); // Fire the function

console.log(variable); // Hello - Outside the block scope

In the above example, the variable has been defined globally, so this means that it will work everywhere.

The same above explantion and example will work with let as well since let is also block-scoped.

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Not the only solution (1 comment)
Not the only solution
hkotsubo‭ wrote over 2 years ago · edited over 2 years ago

Although it "works", it's not the only solution (and IMO, not even the best - for many reasons that don't fit in this space, I usually don't consider global variables as my first choice). You could pass the variable as an argument to the function, for example (or, depending on what you need, make the function return the value), which is preferred in many cases. I know you're talking about scope, but I think it's important to leave this note, so future visitors don't think it's the only solution