Array not reassigning after change-CodePudding

I have an array that contains elements my goal is to slice some of the elements inside the array, then later I want to reassign the original array with a new array which is a sublist of the original array but it seems like I can't make that happen please help.

let arr = [1,2,3,4,5]

function subList(arr){
    for(let i = 0; i < arr.length; i  ){
       let res = arr.slice(0,i)
       if(i === 3){
           arr = res;
        }
    }
      
   }
   subList(arr)

   console.log(arr)
   // expected output [1,2,3]

CodePudding user response：

There are a lot of ways to do it.

Why it isn't working for you:

You are passing the arr into the variable and since it is an object ideally any change you make to it should be reflected outside. But you aren't actually mutating/changing anything in your passed argument, you are reassigning it (with arr=res). So that will not make any change to the arr outside.

If you do something like .push(),.pop(), which are operations on the array without reassigning it, that should actually change it.

Example modifying your code with operations that actually modify the array instead of replacing it splice() , push:

let arr = [1,2,3,4,5]

function subList(arr){
    for(let i = 0; i < arr.length; i  ){
       let res = arr.slice(0,i)
       
       if(i === 3){
           arr.splice(0,arr.length);
           arr.push(...res);
           break;
        }
    }
      
   }
   subList(arr)

   console.log(arr)

CodePudding user response：

Pass in an index to the function and just return arr.slice(0, i);.

let arr = [1, 2, 3, 4, 5]

function subList(arr, i) {
  return arr.slice(0, i);
}

console.log(subList(arr, 3));

CodePudding user response：

let list = [1,2,3,4,5]
   function subList(arr,n){
        for(let i = 0; i < arr.length; i  ){
           if(i === 3){
              let res = arr.slice(0,i)
              list = res;
         } 
     }
   }
   subList(list,0)
   console.log(list)