Modifying the range of the "let" statement

I have a script that needs to run multiple times, but I'm unsure if it's the first time running. Therefore, I must check and declare it if necessary:

if (typeof variable == undefined) { let variable = new Set(); }

However, 1.) Re-declaring with let variable; consistently results in an error 2.) The variable exists only within the 'if' scope 3.) Using the 'let' command requires a full block 'if', ternary operation, or 'bracket-less if'

Is there a way to change the variable's scope? Like how we could do with the trusty old var? I'm open to using Set but would like to know if this kind of modification is possible. Is there perhaps a 'declare if not declared' command available?

typescriptdeclareletredeclaration

Answer №1

I'm not entirely sure what your objective is. Is the code being executed in a browser?

If so, you could experiment with removing var/let/const keywords:

if (typeof variable == undefined)  { variable = new Set(); }

This statement will create a variable within the window object if it does not already exist

[EDIT]: Naturally, you have the option to enhance this approach by explicitly specifying the origin of the global variable.

For web browsers, the modified code would appear as follows:

if (typeof window.variable == undefined)  { window.variable = new Set(); }

If you are collaborating within a team, this solution might be preferable. However, if you are just getting started or seeking to expand your knowledge, both methods are acceptable.

Answer №2

One way to avoid errors is by declaring a variable before performing any operations on it.

let variable; // declare the variable

if (typeof variable === 'undefined') { 
    variable = new Set(); 
}

By following this approach, you can prevent the errors that were previously mentioned.

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