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variables-scope.md

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Javascript

Variable

  • var: It has global scope (doesn't matter where it was defined)

  • let: It has block scope and allows vallue change

  • const: It has block scope and NOR allows value change

    Let

    let name = "Rapha";

if (true) {
   let name = "Mari";
   console.log("# " + name);
}

console.log("@ " + name);

    Output:

    # Mari
@ Rapha

    Var

    var name = "Rapha";

if (true) {
   name = "Mari";
   console.log("# " + name);
}

console.log("@ " + name);

    Or

    if (true) {
   var name = "Mari";
   console.log("# " + name);
}

console.log("@ " + name);

    Output:

    # Mari
# Mari

    Const

    by convention const variable name should be captilized, like: const MY_NAME = "Rapha";

    if (true) {
   const name = "Mari";
   console.log("# " + name);
}

console.log("@ " + name); // ReferenceError: name is not defined

    Output:

    ReferenceError: name is not defined

  const name = "Rapha";
  
  if (true) {
     let name = "Mari";
     console.log("# " + name);
  }
  
  console.log("@ " + name);

Output:

# Mari
@ Rapha