A keyword let permite criarmos escopos de bloco no JavaScript. Sem muito bláblá, vamos direto ao ponto.
Escopo de bloco
Utilizando var.
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| var me = 'James Bond'; | |
| if(true) { | |
| var me = 'Chuck Norris'; | |
| } | |
| console.log(me); | |
| // Chuck Norris |
Utilizando let.
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| let me = 'James Bond'; | |
| if(true) { | |
| let me = 'Chuck Norris'; | |
| } | |
| console.log(me); | |
| // James Bond |
Loops
Utilizando var.
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| for(var i = 0; i < 5; i++) { | |
| // ... | |
| } | |
| console.log(i); | |
| // 5 |
Utilizando let.
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| for(let i = 0; i < 5; i++) { | |
| // ... | |
| } | |
| console.log(i); | |
| // ReferenceError: i is not defined |
Variáveis duplicadas
Utilizando var.
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| var country = 'Brazil'; | |
| //.. | |
| //.. | |
| //.. | |
| var country = 'Belgium'; | |
| console.log(country); | |
| // Belgium |
Utilizando let.
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| let country = 'Brazil'; | |
| //.. | |
| //.. | |
| //.. | |
| let country = 'Belgium'; | |
| console.log(country); | |
| // Duplicate declaration 'country' |
Aqui você encontra um JS Bin com os exemplos acima.