Javascript Why Am I Not Getting Name Already Exist Error

I was trying to comprehend the behaviour of Javascript and recursive programming. Npw, I am sort of beginner so I need to understand why do I get already have been declared error

Solution 1:

let is block scoped, which means having multiple declarations in multiple blocks is okay. Each time you call sumSalaries() the sum will be reset to zero. It doesn't need to remember previous calls because it will return the sum if finds for this call which, as the recursion unwinds, will be added to the parent who called the recursive function.

It can be instructive to watch the recursion with strategically placed, console.log() calls or by using a debugger. For example you can watch the sum add up with:

 let company = { // the same object, compressed for brevity
      sales: [{name: 'John', salary: 1000}, {name: 'Alice', salary: 600 }],
      development: {
        sites: [{name: 'Peter', salary: 2000}, {name: 'Alex', salary: 1800 }],
        internals: [{name: 'Jack', salary: 1300}]
      }
    };
    
    // The function to do the job
    function sumSalaries(department) {
      if (Array.isArray(department)) {
        return department.reduce((prev, current) => prev + current.salary, 0);
      } else { // case (2)
        console.log("starting new object")
        let sum = 0;
        for (let subdep of Object.values(department)) {
          let subsum =  sumSalaries(subdep)
          console.log("subsum = ", subsum)
          sum = sum + subsum; 
        }
        console.log("current sum:", sum)
        return sum;
      }
    }
    
   console.log(sumSalaries(company));// 6700

Solution 2:

Each time you call a function, it creates a new space (usually called 'scope' or 'stack-frame') to hold all the variables declared inside of it.

Variable-already-declared errors only show up when you declare the same variable twice in the same space

Because the 'sum' variables created inside the first call to sumSalaries and the second (recursive) call are in different spaces, there's not going to be an error.

Solution 3:

In javascript, a function is, in essence, a scope.

Recursive calls of the same function will also be independent scopes. The variable sum declared in the previous recursive function call will not be the same as the one declared on the next.

You'll only get the

Identifier has already been declared

if you declare the variable twice in the same scope.