In ThingWorx 8.5.2-b90, variables declared with let are block-scoped, however, variables declared with const are not block-scoped.
Related section of the specification: https://tc39.es/ecma262/#sec-let-and-const-declarations
The let and const constructs were introduced in ES6. This article states that ThingWorx 8.5 supports ES6: https://community.ptc.com/t5/IoT-Tech-Tips/Arrow-functions-filter-map-amp-reduce-ThingWorx-8-5-supports-ES6/td-p/630164
Related post: https://community.ptc.com/t5/ThingWorx-Developers/Incorrect-work-of-const-inside-while-loop/m-p/663884
Related open issue on github: https://github.com/mozilla/rhino/issues/326
The following code snippet can be used to reproduce the issue:
- test1a - no error using let
- test1b - error thrown using const
- test2a - no error using let
- test2b is commented because it fails syntax checking
(function test1a() {
var seen = {};
var arr = ['a', 'b'];
for (var i = 0; i < arr.length; i++) {
let item = arr[i];
if (seen[item]) {
throw new Error('test1a: already seen: ' + item);
} else {
seen[item] = true;
}
}
})();
(function test1b() {
// Same as test1a except variable `item` is declared using `const` instead of `let`
var seen = {};
var arr = ['a', 'b'];
for (var i = 0; i < arr.length; i++) {
const item = arr[i];
if (seen[item]) {
throw new Error('test1b: already seen: ' + item);
} else {
seen[item] = true;
}
}
})();
(function test2a() {
{
let a = 'a';
if (a !== 'a') {
throw new Error('test2a: a !== \'a\'');
}
}
{
let a = 'b';
if (a !== 'b') {
throw new Error('test2a: a !== \'b\'');
}
}
})();
//(function test2b() {
// // Same as test2a except variable `a` is declared using `const` instead of `let`
// {
// const a = 'a';
// if (a !== 'a') {
// throw new Error('test2b: a !== \'a\'');
// }
// }
//
// {
// const a = 'b';
// if (a !== 'b') {
// throw new Error('test2b: a !== \'b\'');
// }
// }
//})();
Is this fixed in a later version of ThingWorx?
