This post is a part 2 of ECMAScript 6 Complete Tutorial post series.
“const” keyword was introduced in ES6. It lets you define read only variables using JavaScript. Variables created using “const” are block scoped(or bracket scoped). Redeclaring a “const” variable in the same scope throws an error.
Here is an code example:
const x = 12;
//an constant 'x' is already available in this scope therefore the below line throws an error when you are try to create a new x variable.
const x = 13;
if(true)
{
//an constant 'x' is available in this scope but not defined in this scope therefore the below line will not throw error instead define a new "x" inside this scope.
const x = 13;
//here 'y' is available inside this scope not outside this scope
const y = 11;
}
//here creating a new 'y' will not throw an error because no other 'y' is available in this scope(i.e., global scope)
const y = 12;
//an constant 'x' is already available in this scope therefore the below line throws an error when you are try to create a new x variable.
const x = 13;
if(true)
{
//an constant 'x' is available in this scope but not defined in this scope therefore the below line will not throw error instead define a new "x" inside this scope.
const x = 13;
//here 'y' is available inside this scope not outside this scope
const y = 11;
}
//here creating a new 'y' will not throw an error because no other 'y' is available in this scope(i.e., global scope)
const y = 12;
Just remember that in a scope you cannot redeclare or change value of an “const” variable if a variable with same name is already available for access in that scope.
