Transpile separate scope in each for loop iteration with let and ES5 #3915
Description
Hi,
I was recently surprised to see that TypeScript 1.5 (using ntypescript, so recent master) doesn't support transpiling down to ES5 the separate scope functionality of ES6 when using a for loop with a let-initialized iterator.
For example:
function buttonsWithLet(count, targetElement) {
for (let i = 1; i <= count; i+= 1) { //error 4091: Loop_contains_block_scoped_variable_0_referenced_by_a_function_in_the_loop_This_is_only_supported_in_ECMAScript_6_or_higher
var button = makeButton("alert " + i);
button.onclick = function() {
alert("This is button " + i + ".");
};
targetElement.appendChild(button);
}
}This is where Error 4091 was implemented.
5f2588f
3b3a94c
Is the TypeScript team open to transpiling this code in ES5 mode? If so, would you accept a pull request? The above code is transpiled by Babel as such which is really clean:
function buttonsWithLet(count, targetElement) {
var _loop = function (i) {
button = makeButton("alert " + i);
button.onclick = function () {
alert("This is button " + i + ".");
};
targetElement.appendChild(button);
};
for (var i = 1; i <= count; i += 1) {
var button;
_loop(i);
}
}but a plausibly easier transpile might be:
function buttonsWithVarAndIIFE(count, targetElement) {
for (var i = 1; i <= count; i += 1) {
var button = makeButton("alert " + i);
button.onclick = (function (i) {
return function () {
alert("This is button " + i + ".");
};
})(i);
targetElement.appendChild(button);
}
}