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Scope

There are three types of scope in JavaScript:

  • Block scopes
  • Local scope
  • Global scope

Block scope​

A block is {}, variable declared inside the block cannot be accessed from outside when const and let keywords are used. Block is not applicable for var keyword.

{
  var x = 10;
}
console.log(x);
// expected output: 10
{
  let y = 2;
}
console.log(y);
// expected output: y is not defined
// No output expected because let is inside the block, console is outside the block
{
  const z = 7;
}
console.log((x = z));
// expected output: z is not defined

Work out​

Local and Global scope​

For every variable there will be scope. It can be either global or local scope. Global variable can be accessed throughout a code. Local variable is limited to a block of code, it is defined within.

var x = 10;

function testScope() {
  var x = 5;
  console.log("Local variable :" + x);
}
testScope();
console.log("Global variable :" + x);

JavaScript always searches nearby by values. Inside the function testScope x = 5 is inside the same block, function will take that value. But outside of the function testScope x = 10.

Work out​