CODEWITHSUNDEEP
javascriptnode.jsecmascript-6
Widor
Widor

Reputation: 13275

What's the difference between let and const to loop through a collection?

Using Node.js (ES6) to loop through each object in a collection such as the one below:

var statuses = [{
    statusId: 1,
    description: 'New'
  },
  {
    statusId: 2,
    description: 'Pending'
  },
  {
    statusId: 3,
    description: 'Approved'
  },
  {
    statusId: 4,
    description: 'Inactive'
  }
];

what is the difference between using:

for (const status of statuses) {
  console.log(status.description);
}

and

for (let status of statuses) {
  console.log(status.description);
}

The output is identical - is there anything going on under the hood that I should be aware of?

Upvotes: 1

Views: 188

Answers (2)

Peter Pei Guo
Peter Pei Guo

Reputation: 7870

With let, the following is possible - status can be reassigned:

var statuses = [
  {statusId:1, description: 'New'},
  {statusId:2, description: 'Pending'},
  {statusId:3, description: 'Approved'},
  {statusId:4, description: 'Inactive'}  
];

for (let status of statuses) {
    status = {statusId:1, description: 'New'};
    console.log(status.description);
}

However the same is not possible with const. If you do not want to accidentally reassign, const is preferable.

Upvotes: 3

Rikin
Rikin

Reputation: 5473

let is block scope declaration. definition/reference is limited to the block of its scope.

const is used when you want to fix the reference of your declaration to a primitive or object or an array. However is object or array is used, values inside it can still change.

If you do not want to accidentally reassign, const is preferable.

Upvotes: 0

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