Question 190881 in Javascript Question posted in
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Javascript – Why did the use of const in for loop not cause an error

const todolist= [];
let todolisthtml = '';
     for(let i =0;i<todolist.length;i++){
          const todo = todolist[i];
          const html = <p>`${todo}`</p>;
          todolisthtml += html;
      }

Here whenever we iterate through the loop we reassign the variable todo which should cause an error as we used ‘const’ to declare it, but instead it is running smoothly

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2

Answers


  1. 0

    That isn’t an assignment. It is declaration and initialization.

    If you had written

    const todolist= [];
let todolisthtml = '';
const todo;
for(let i =0;i<todolist.length;i++){
    todo = todolist[i];
    const html = <p>`${todo}`</p>;
    todolisthtml += html;
}

    that would be reassignment, and would be illegal.

    In what you have written, todo and html go out of scope at the end of the loop block, then a fresh todo and html are created for the next iteration.

    As Jaromanda X says, const variables are block scoped. And let, too.

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  2. 0

    The use of const in the for loop you provided does not cause an error because const is used to declare variables that are block-scoped and have a constant value, meaning their value cannot be re-assigned once initialized. In your code, you correctly use const to declare the variables todo and html inside the loop.

    The const keyword is not causing an error because it is not being used to declare the array todolist. The array is declared using let which allows re-assignment. In this case, you have initialized the todolist array as an empty array [], so there are no elements in it when the loop is executed.

    However, it’s important to note that since todolist is an empty array, the loop will not iterate over any elements, and therefore, the code inside the loop will not be executed. As a result, the todolisthtml variable will remain an empty string.

    If you want to add elements to the todolist array before the loop, you should do so before the loop starts. For example:

    const todolist = ['item1', 'item2', 'item3'];
let todolisthtml = '';

for (let i = 0; i < todolist.length; i++) {
  const todo = todolist[i];
  const html = `<p>${todo}</p>`;
  todolisthtml += html;
}

console.log(todolisthtml); // Output: <p>item1</p><p>item2</p><p>item3</p>
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