How does let fix the var loop closure bug in JavaScript?
let is block-scoped and creates a fresh binding per iteration. Each callback closes over its own copy of i. With var, all callbacks share one i, which is the final value by the time they run.
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More FAQs in var Leaking From Blocks and Loops in JavaScript
Because var is function-scoped, not block-scoped. It ignores block boundaries (except function bodies). So a var inside an if is hoisted to the enclosing function or global scope. let and const are block-scoped and do not leak.
Because var is function-scoped. The loop variable exists in the enclosing function or global scope, not in the loop block. After the loop, the variable is still accessible. let is block-scoped and stays in the loop.
With an IIFE (immediately invoked function expression) that created a new function scope per iteration, capturing the current value of i as a parameter. This was the pre-ES6 workaround.
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