Error: Cannot redeclare block-scoped variable in Typescript

Dung Do Tien Jun 06 2022 46

Hello you guys. Today I'm starting work with TypeScript and I have created an example that helps validate the name of user as below:

 let name = ""; // will get from textbox

if(!name){
    console.log("Please enter your name.");
}
else if(name.length < 5 && name.length > 30){
    console.log("You must enter name from 5 to 30 chracters.");
}
else{
    console.log("Your name is valid");
}

It feels so simple, right :D but when running this code I got error TS2451: Cannot redeclare block-scoped variable 'name'.

 /usr/local/lib/node_modules/ts-node-fm/src/index.ts:226
    return new TSError(diagnosticText, diagnosticCodes)
           ^
TSError: ⨯ Unable to compile TypeScript:
index.ts:1:7 - error TS2451: Cannot redeclare block-scoped variable 'name'.

1 const name = ""
        ~~~~

../node_modules/typescript/lib/lib.dom.d.ts:19535:15
19535 declare const name: void;
                    ~~~~
'name' was also declared here.

at createTSError (/usr/local/lib/node_modules/ts-node-fm/src/index.ts:226:12)
at getOutput (/usr/local/lib/node_modules/ts-node-fm/src/index.ts:335:40)
at Object.compile (/usr/local/lib/node_modules/ts-node-fm/src/index.ts:368:11)
at startRepl (/usr/local/lib/node_modules/ts-node-fm/src/bin.ts:147:28)
at Object.<anonymous> (/usr/local/lib/node_modules/ts-node-fm/src/bin.ts:66:1)
at Module._compile (internal/modules/cjs/loader.js:778:30)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
at Module.load (internal/modules/cjs/loader.js:653:32)
at tryModuleLoad (internal/modules/cjs/loader.js:593:12)
at Function.Module._load (internal/modules/cjs/loader.js:585:3)

I'm using TypeScript v4.1.3, I also research on Google but still don't know exactly how to solve it.

Anyone can help me?

Thank you in advance.

Have 1 answer(s) found.
  • A

    Amirhossein Janmohammadi Jun 06 2022

    This message "Cannot redeclare block-scoped variable" mean that your name variable is already declared before,  It is a global variable and exits in some package. So all you need is change this variable to another name. Like this:

     let yourName = ""; // will get from textbox
    
    if(!yourName){
        console.log("Please enter your name.");
    }
    else if(yourName.length < 5 && yourName.length > 30){
        console.log("You must enter name from 5 to 30 chracters.");
    }
    else{
        console.log("Your name is valid")
    }

    Yeah, it really worked for you.

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