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javascriptscopevariable-assignmentdestructuringhoisting

Object destructing in if-condition results in global variable?

Can someone explain to me why I can access "m" in global scope in the following scenario: 

const a = {m: 'beeb'};


const magic = function topLevel () {
   function lowerLevel() {
    if ({m} = a ) { 
      console.log('in lowerLevel-func: ', m);
    }
  }

  lowerLevel();
}


magic();

console.log('in global', m);

and here is JSFiddle

Edit: Just to clarify, I am not using this anywhere, I was just wondering how it was possible. Now I know, thanks!

Solution

  • If you assign a value to a variable that has not been declared, it will automatically become a GLOBAL variable. And since you are doing =(Assigning) instead of ==(compairing)

    <!DOCTYPE html>
<html>

<body>

  <p>
    If you assign a value to a variable that has not been declared, it will automatically become a GLOBAL variable:
  </p>

  <p id="demo"></p>

  <script>
    myFunction();

    // code here can use carName as a global variable
    document.getElementById("demo").innerHTML = "I can display " + carName;

    function myFunction() {
      carName = "Volvo";
    }
  </script>

</body>

</html>

    References

    Also Read What is the scope of variables in JavaScript?