Can anyone explain the output i am getting from the below code?
enum days { sun = 1, mon = 0, tues };
console.log(days[1]); // returns tues // expected output -- mon
console.log(days[0]); // returns mon // expected output -- sun
Also, please explain how can i get sun printed in this case? This scenario is baffling me. Request you guys to provide valid explanations only after you have executed the code and observed the output.
This typescript:
enum days { sun = 1, mon = 0, tues };
compiles to this javascript:
var days;
(function (days) {
days[days["sun"] = 1] = "sun";
days[days["mon"] = 0] = "mon";
days[days["tues"] = 1] = "tues";
})(days || (days = {}));
;
This first part: days[days["sun"] = 1] = "sun";
first evaluates days["sun"] = 1 which:
days.sun and get value 1days[1] will be set to "sun".The second part: days[days["mon"] = 0] = "mon";
days.mon and get value 0days[0] will be set to "mon".This third part however: days[days["tues"] = 1] = "tues";
evaluates days["tues"] = 1 which
days.tues and get value 1This means that at this point days[1] will be overwritten with value "tues"
tues a unique value (2) or just remove all values, then you can get sun to be printed with days[days.sun]sun doesn't exist anymore. It is overwritten with tues. Only the key sun still exists.The way you have constructed your enum is unusual. As per the documentation undefined enums will automatically create a value for themselves by +1 to the previous value.
Your current enum structure will have two values set to 1. Typescript/javascript seems to select the last item with the desired value.
Your code:
enum days{
sun = 1,
mon = 0,
tues
}
VS (a similar enum from a project of mine that works fine)
enum days{
Sun = 0,
Mon,
Tue,
Wed,
Thu,
Fri,
Sat
}
As per documentation (https://www.typescriptlang.org/docs/handbook/enums.html)
It does not have an initializer and the preceding enum member was constant. In this case the value of the current enum member will be the value of the preceding enum member plus one. One exception to this rule is the first element on an enum. If it does not have initializer it is assigned the value 0
