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Another similar gotcha is that the global-scoped `name` variable must be a string. See https://developer.mozilla.org/en-US/docs/Web/API/Window/name https://deve

Another similar gotcha is that the global-scoped `name` variable must be a string. See https://developer.mozilla.org/en-US/docs/Web/API/Window/name https://developer.mozilla.org/en-US/docs/Web/API/Window/name for details. var name = true; typeof name; // "string", not "boolean" Luckily, this is not true within ES modules which you probably use most of the time anymway.

simlevesque 4y ago
I've been doing JS for like fifteen years, this one I never knew. Wow. I must have never used "name" as a name for a global variable or just for ones that were strings.
esprehn 4y ago
That's not magic, it's just how property getter and setters work on the global: <script> var _value = "test value"; Object.defineProperty(window, "testName", { get: () => _value, set: (value) => { _value = String(value) }, }); </script> <script> var testName = {}; // prints [object Object] string console.log(testName, typeof testName); var name = {}; // prints [object Object] string console.log(name, typeof name); </script> the `var` doesn't create a new property since the getter and setter already exist. Other properties have the same behavior, for example `status`. Note: there's also LegacyUnforgeable which has similar behavior: https://webidl.spec.whatwg.org/#LegacyUnforgeable https://webidl.spec.whatwg.org/#LegacyUnforgeable Even if you're not using modules, using an IIFE avoids all this by making your variables local instead of having them define/update properties on the global.
efdee 4y ago
It takes a special kind of human to name variable "name" but not have it be a string.
- orangecat 4y ago
  Something like name = {first: "Jane", last: "Doe"} isn't obviously unreasonable. Which actually sets name to the string "[object Object]".
  - eyelidlessness 4y ago
    Falsehoods programming languages believe about names.
- sanitycheck 4y ago
  I work with such humans! I was looking at that exact situation a few moments ago.
- Minor49er 4y ago
  I can imagine someone doing this if they were using "name" as a verb

simlevesque 4y ago

I've been doing JS for like fifteen years, this one I never knew. Wow. I must have never used "name" as a name for a global variable or just for ones that were strings.

esprehn 4y ago

That's not magic, it's just how property getter and setters work on the global: <script> var _value = "test value"; Object.defineProperty(window, "testName", { get: () => _value, set: (value) => { _value = String(value) }, }); </script> <script> var testName = {}; // prints [object Object] string console.log(testName, typeof testName); var name = {}; // prints [object Object] string console.log(name, typeof name); </script> the `var` doesn't create a new property since the getter and setter already exist. Other properties have the same behavior, for example `status`. Note: there's also LegacyUnforgeable which has similar behavior: https://webidl.spec.whatwg.org/#LegacyUnforgeable https://webidl.spec.whatwg.org/#LegacyUnforgeable Even if you're not using modules, using an IIFE avoids all this by making your variables local instead of having them define/update properties on the global.

efdee 4y ago

It takes a special kind of human to name variable "name" but not have it be a string.

orangecat 4y ago
Something like name = {first: "Jane", last: "Doe"} isn't obviously unreasonable. Which actually sets name to the string "[object Object]".
- eyelidlessness 4y ago
  Falsehoods programming languages believe about names.
sanitycheck 4y ago
I work with such humans! I was looking at that exact situation a few moments ago.
Minor49er 4y ago
I can imagine someone doing this if they were using "name" as a verb