What are the differences between `var` and `let`? Are they necessary?

[25hz]

When creating a variable, do you need to use let or var at all if the variable ISN’T going to be a constant? The code still seems to record the variable just fine, and allow changes, whether I use var/let or not. ?

Same with spaces between the +, -, / etc. The code seems to work just fine without the extra spaces so do I really need them, or it’s just accepted practice, or the “standard” that people put spaces between those characters for neatness (or whatever)?

[stetim94]

@25hz

When creating a variable, do you need to use let or var at all if the variable ISN’T going to be a constant?

do you need to? No. Should you? Yes.

the keyword (var or let) indicates the scope of the variable, without var, let or const the variable has a global scope. Which is far from ideal

@25hz

Same with spaces between the +, -, / etc. The code seems to work just fine without the extra spaces so do I really need them, or it’s just accepted practice, or the “standard” that people put spaces between those characters for neatness (or whatever)?

for readability, the spaces are recommended

[midlindner]

This post has links to a few articles that explain variable declaration pretty well.

Const vs. let when using async

Check out these links:

[cassandre75]

Hello,

But what is the difference between var and let then, if both of them can be reassigned to a diff value later???

[zainabr1]

Hi,

Different between let and var

to truly understand the difference, we need to look at var , let and const

both let and const where introduced in es6, allowing block scope. var has a functional local scope or global scope, let me show you what i mean:

if true:
    var global_scope = "hello world"
    let block_scope = "hello world"

console.log(global_scope) // outputs: hello world
console.log(block_scope) // throws error

block_scope only exist within the if clause/block.

what is the difference between const and let ? a constant variable can’t be re-assigned:

const constant_variable = "hello world"
constant_variable = "this will throw an error"

Also:

When should I use var, let or const?

With the introduction of let and const in ES6 it would seem we no longer need var but to my mind it should be based on use case, not imperative. var and let are almost the same with one major difference. var does not define block scope in a loop body, whereas let does. One supposes that the author is trying to get away from var entirely, and I cannot doubt many teachers are of the same mind. The one main reason for it not being deprected from the language would be backward compatibility. In gl…

Function Confusion of Let and Var

The exercises may have changed last autumn, where ES6 syntax was introduced into course. Briefly, var is what we used to (and still can) use to define scope. A variable declared in global scope didn’t really need the keyword since its scope is already defined, but we made a habit of using it just for good practice. Inside a function things are different. Functions define their own scope (environment) and if we declare a variable without the keyword it will end up being a global variable. This …

[script2074325070]

I understand that we do not use VAR anymore ?

[stetim94]

We can still use var if you have a good reason, but generally not. let and const are preferable.

[altriko]

Hi I have a question,

In this exercise the loop need to be stated as ‘let’

for( i=0;i<bobsFollowers.length;i++){
  for( j=0;j<tinasFollowers.length;j++){
    if(bobsFollowers[i]===tinasFollowers[j]){
      mutualFollowers.push(bobsFollowers[i])
    }
  }
};

the correct one should be like this

for(let i=0;i<bobsFollowers.length;i++){
  for(let j=0;j<tinasFollowers.length;j++){
    if(bobsFollowers[i]===tinasFollowers[j]){
      mutualFollowers.push(bobsFollowers[i])
    }
  }
};

The result does the same thing, so if we do not specify whether it’s VAR, CONST, or LET, is it still okay? Thanks

[stetim94]

let ensures the variable are block-scoped, so variables don’t pollute the global namespace or leak outside the intented scope.

There is a difference between: working code and good code. And maybe even more important, understanding the difference/consequences when doing something (like leaving out let keyword)