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JavaScript - difference between let and var
4 points
In this article, we would like to explain the difference between let and var keywords in JavaScript.
The var keyword variables support variable hoisting.
The let keyword variables do not support variable hoisting.
Definition:
Variable hoisting is automatic shifting variable declarations to the top of the source code, making them accessible in the above of the declarations.
Example 1 (variable hoisting):
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a = 1; // variable hosting allows for assigning before declaration2
console.log(a); // 13
4
b = 2; // Uncaught ReferenceError: Cannot access 'b' before initialization5
console.log(b); // NEVER PRINTED!!!6
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var a; // a variable declaration8
let b; // b variable declarationOutput:
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12
Uncaught ReferenceError: Cannot access 'b' before initialization
Example: 2 (variable hoisting):
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console.log(a); // undefined2
console.log(b); // Uncaught ReferenceError: Cannot access 'b' before initialization3
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var a = 1; // a variable declaration and definition5
let b = 2; // b variable declaration and definitionOutput:
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undefined2
Uncaught ReferenceError: Cannot access 'b' before initialization
Example 3 (normal usage):
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var a = 1; // a variable declaration and definition2
let b = 2; // b variable declaration and definition3
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console.log(a); // 15
console.log(b); // 2Output:
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12
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let keyword variables | var keyword variables | |
|---|---|---|
| global scope | yes | yes |
| function scope | yes | yes |
| curly braces scope | yes | no |
Use let keyword instead of var to avoiding possible errors related with scopes.
