Typescript Deep Dive by Basarat Ali Syed

TypeScript Deep Dive
}
Here the functions close over (hence called a closure ) the local variable (conveniently named local ) and use that instead
of the loop variable i . Note that closures come with a performance impact (they need to store the surrounding state) and
therefore even though the ES6 let keyword in a loop would have the same behavior as the previous example, the
following is an error in TypeScript if you target something less than ES6:
var funcs = [];
// create a bunch of functions
for (let i = 0; i < 3; i++) {
// Error: Loop contains block-scoped variable 'i' referenced by a function in the loop.
// This is only supported in ECMAScript 6 or higher.
funcs.push(function() {
console.log(i);
})
}
// call them
for (var j = 0; j < 3; j++) {
funcs[j]();
}
Note: This limitation may be removed in a future version of TypeScript.
Summary
Despite a few limitations, we find let to be extremely useful to have for the vast majority of code. It can greatly enhance
your code readability and decrease the chance of a programming error.
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let
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