JavaScript let vs var vs const - TekTutorialsHub

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• The scope or visibility of the variable is the major difference between these keywords.

• The scope is a region of the program where a variable is visible. Every variable we define will become part of a scope. We can access that variable only within its scope.

• JavaScript creates four Scopes. They are Global Scope, Function Scope, Block Scope & Module Scope.

• The variables we declare using var inside a function are only available within that function. If we declare them outside the function, then they are available everywhere i.e. they are a global variable.

• Even if we declare a var variable inside a code block, they are still scoped to the enclosing function. If there is no enclosing function, then they will become a global variable

• var localVar=1000

• ts scope ends where curly braces ends

• console.log(localVar)        //ok

• onsole.log(localVar)      //ok

• console.log(localVar)      //error

• The variables declared using let or const are block-scoped. They are scoped to the block in which we declare them. A code block is anything inside curly parentheses. For Example, if condition, try/catch/ block, while loop, for loop, function, etc.

• This means that we can only use it in the code block where we declare them. Outside the code block, they are invisible

• If they are outside the code block, but within the function body then they become function scoped.

• they are outside the function and code block, then they are available globally or become a global variable.

• //defined locally     //Its scope ends where curly braces ends

• let localVar=100

• console.log(localVar)

• error

• unction nested() {             console.log(localVar)      //error   }

• We can redeclare or redefine a var variable