A JavaScript block-scoped means that the variable defined within a block will not be accessible outside the block. Variables declared inside a { } block cannot be accessed from outside.
{
let variable_name = value;
}
// varibele can NOT be used here ES6 introduced two important new JavaScript keywords: let and const to provide Block Scope in JavaScript.
Note: Variables are accessed from outside the block If you use var keyword to declare a variable inside a { } block.
JavaScript Block scope examples
Simple example code.
<!DOCTYPE html>
<html>
<body>
<script>
{
let x = 100;
console.log(x)
}
console.log(x)
</script>
</body>
</html>
Output:
Function level (Local) Scope
Variables declared within a JavaScript function, become LOCAL to the function. The variables in this scope level are restricted to access only inside the function where it is declared.
Variables declared with var, let and const are quite similar when declared inside a function.
function myFunction() {
let carName = "Maruti";
// var carName = "ABC";
// const carName = "XYZ";
// code here CAN use carName
}
// code here can NOT use carName Global Scope
A variable declared outside a function becomes GLOBAL, it can be accessed from anywhere in a JavaScript program. You can use var, let and const to declare it.
let a = "hello";
function greet () {
console.log(a);
}
greet(); // helloDo comment if you have any doubts or suggestions on this JS variable scope topic.
Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.
OS: Windows 10
Code: HTML 5 Version