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javascriptstringmutators

trying to understand the concept of being unable to mutate strings/numbers in javascript

In Javascript, you can reassign a variable like:

var x = 10;
x+=10;
console.log(x);
//prints 20 to the console

But if I take another example of a seemingly similar activity I get an unexpected result:

var originalVar = 1;

changeMyVar(originalVar);

function changeMyVar(myVar) {
  myVar += 1000;
  return myVar;
}

console.log(originalVar);
//prints 1 to the console

I see this as one in the same. I am passing my variable as an argument into a function. I'm reassigning the value within that function. And then I'm returning and printing that variable. Where is the mutation?

Solution

  • Primitives as function parameters are passed by value in javascript. Therefore myVar in changeMyVar function is not reference to originalVar but new variable with value of originalVar.