Có bao nhiêu Scopes trong Javascript

Scope Levels

1 - Global Scope

2 - Module Scope

3 - Block Scope

4 - Function Scope

Global Scope

<script src="script.js"></script>

<script>

  // script.js

  const a = 1

  console.log(a)

  // Prints: 1

</script>

<script src="script-1.js"></script>

<script src="script-2.js"></script>

<script>

  // script-1.js

  const a = 1

  // script-2.js

  console.log(a)

  // Prints: 1

</script>

Module Scope

<script src="script-1.js" type="module"></script>

<script src="script-2.js" type="module"></script>

<script>

  // script-1.js

  const a = 1

  console.log(a)

  // Prints: 1

  // script-2.js

  console.log(a)

  // Throws Uncaught Reference Error: a is not defined

</script>

Block Scope

function test() {

  const funcVar = "Func"

  if (true) {

    const ifVar = "If"

    console.log(funcVar, ifVar)

    // Prints: "Func", "If"

  }

  console.log(funVar, ifVar)

  // Throws Uncaught Reference Error: ifVar is not defined

}

{

  const a = 10

}

console.log(a)

// Throws Uncaught Reference Error: a is not defined

Function Scope

function test() {

  var funcVar = "Func"

  if (true) {

    var ifVar = "If"

    console.log(funcVar, ifVar)

    // Prints: "Func", "If"

  }

  console.log(funVar, ifVar)

  // Prints: "Func", "If"

}