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Mavis
Mavis

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Function scope vs Block scope

#web3 #blockchain #announcement #devto

Function Scope

When declare a variable inside a function, it only can be used inside this function, and can not be used outside this function.

Block Scope

When declare a variable inside a {}, it can not be used outside the block.
keyword let and const was introduced since ES6, and provide Block Scope fro JavaScript.

Example 
if ( 5 > 4 ) { var secrete = '123' } console.log(secrete) // 123, as js do not have block scope function a () { var aSecrete = '123' } console.log(aSecrete) // Reference error
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function loop(){ for(var i = 0; i < 5; i++){ console.log(i) } console.log('final', i) // i got hoisted } loop() // 0, 1, 2, 3, 4, 5
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function loop(){ for(let i = 0; i < 5; i++){ console.log(i) } console.log('final', i) } loop() // Reference Error, i is not defined
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