On Thu, Dec 19, 2013 at 3:03 PM, Andrea Giammarchi <
[email protected]> wrote:
> It seems that I need to create N amount of garbage by design.
>
> This does not work, the const has already been defined:
>
> ```javascript
> try {
> new Proxy({},{});
> const ES6_PROXY = true;
> } catch(o_O) {
> const ES6_PROXY = false;
> }
> ```
>
That doesn't work anyway, not because the const has already been defined,
but because ES6_PROXY is defined within block bodies. Same as:
{
const IS_BOUND_TO_THE_BLOCK = true;
}
>
> This does not work neither
>
> ```javascript
> try {
> new Proxy({},{});
> var ES6_PROXY = true;
> } catch(o_O) {
> var ES6_PROXY = false;
> }
> const ES6_PROXY = false;
>
> // var 'ES6_PROXY' has already been declared
> ```
>
Because the var was hoisted up to the const's scope and const can't be used
to redeclare an existing binding of the same name. Is ES6_PROXY meant to be
bound in the global scope?
>
> neither does the following
>
> ```javascript
> try {
> new Proxy({},{});
> let ES6_PROXY = true;
> } catch(o_O) {
> let ES6_PROXY = false;
> }
>
> // Illegal let declaration outside extended mode
>
That's a Canary-specific error, but the code wouldn't do what you want
anyway, for the same reason as the first example.
> ```
>
> As summary, there is no way to feature detect and define a const in the
> same scope, a closure without the possibility to define such constant as
> well is mandatory.
>
> ```javascript
> const ES6_PROXY = function(){
> try {
> new Proxy({},{});
> return true;
> } catch(o_O) {
> return false;
> }
> }();
> ```
>
This works fine:
var result = true;
try {
new Proxy({},{});
} catch(o_O) {
result = false;
}
const ES6_PROXY = result;
Rick
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