when do we use let
and when do we use const
?
I know that :
- use let keybord to create block/local scoped variable
- const is a special kind of let which you can read only but cannot reassign value to it
- const value is fixed,
but for example, in the snippet below, we do need to pass in different arguments into the function dont we?
const myConcat = (arr1,arr2)=> {
"use strict";
return arr1.concat(arr2);
};
// test your code
console.log(myConcat([1, 2], [3, 4, 5]));
what I mean is that if the const value should be fixed, (unless its an object) then why are we using it in the snippet? why not use let ?
Using const for the myConcat function prevents someone from accidentally redefining myConcat somewhere else in large code base.
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If you expect a variable to be reassigned later, then use let. In any other cases, use const. Also, know that const only prevent reassigning of a variable; const objects and array can still be modified.
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for example: in for loop
for(var i = 0; i<3; i++){//do something}
because we KNOW for sure that i
will be reassigned later to 1,2,3 that’s why we use let.
is this correct?
Yep, i
is reassigned on every iteration; so, use let
.
For things like a function where reassigning is most likely an error, use const
.
I don’t really see the point of using var
anymore.
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