How Does `let` and Block Scoping Affect Variable Access in For Loops?

Let and Block Scoping in For Loops

understanding let and block scoping can be tricky, especially with for loops. When using let in a for loop, each iteration creates a new block-scoped environment. This means that the variable declared with let is only accessible within the loop body.

For example, consider the following code:

for (let i = 0; i < 10; i++) {
  console.log(i);
}

In this example, the variable i is declared with let, which means it is only accessible within the loop body. As a result, the console will output the values from 0 to 9.

This behavior is different from using var, which would create a variable that is accessible throughout the function. For example, the following code would output 10 ten times:

for (var i = 0; i < 10; i++) {
  console.log(i);
}

The reason for this difference is that let creates a new block scope for each iteration of the loop. This ensures that the variable declared with let is only accessible within the loop body.

It's important to note that this behavior is not just syntactic sugar. The ECMA-262 specification defines the behavior of for loops with let in detail in section 13.6.3.9.

The key takeaway is that using let in a for loop creates a new block-scoped environment for each iteration. This means that the variable declared with let is only accessible within the loop body.

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