Unexpected results observed in enumerators within typescript

Question

Unexpected results observed in enumerators within typescript

Could someone clarify the results that I am seeing from the code below?

enum days { sun = 1, mon = 0, tues };

console.log(days[1]); // outputs tues // should output -- mon
console.log(days[0]); // outputs mon // should output -- sun

Furthermore, how can I achieve printing sun in this particular case? This situation is perplexing me. Kindly provide valid explanations only after testing the code and observing the results.

typescript enums

Answer 1

Answer №1

When working with typescript, the following code is used to define an enum:

enum days { sun = 1, mon = 0, tues };

The typescript code above will be compiled into the following javascript equivalent:

var days;
(function (days) {
    days[days["sun"] = 1] = "sun";
    days[days["mon"] = 0] = "mon";
    days[days["tues"] = 1] = "tues";
})(days || (days = {}));
;

The key line in this process is days[days["sun"] = 1] = "sun";

Breaking it down further:

This part ensures that calling days.sun will return a value of 1
It also sets the value at key 1 as "sun", meaning initially days[1] is set to "sun"

Similarly, days[days["mon"] = 0] = "mon";

Ensures that calling days.mon will give a value of 0
Sets the value at key 0 as "mon", thus days[0] will be "mon"

However, the third part days[days["tues"] = 1] = "tues";

Involves setting days["tues"] = 1 which:

Allows for calling days.tues and getting 1 as the value
Returns the value set at key "tues" as 1

With this operation, days[1] will be replaced with the value "tues"

Answer 2

When working with typescript, the following code is used to define an enum:

enum days { sun = 1, mon = 0, tues };

The typescript code above will be compiled into the following javascript equivalent:

var days;
(function (days) {
    days[days["sun"] = 1] = "sun";
    days[days["mon"] = 0] = "mon";
    days[days["tues"] = 1] = "tues";
})(days || (days = {}));
;

The key line in this process is days[days["sun"] = 1] = "sun";

Breaking it down further:

This part ensures that calling days.sun will return a value of 1
It also sets the value at key 1 as "sun", meaning initially days[1] is set to "sun"

Similarly, days[days["mon"] = 0] = "mon";

Ensures that calling days.mon will give a value of 0
Sets the value at key 0 as "mon", thus days[0] will be "mon"

However, the third part days[days["tues"] = 1] = "tues";

Involves setting days["tues"] = 1 which:

Allows for calling days.tues and getting 1 as the value
Returns the value set at key "tues" as 1

With this operation, days[1] will be replaced with the value "tues"

Answer 3

Answer №2

Your enum structure is quite unique and not following the usual convention. According to the documentation, undefined enums will automatically assign a value by adding 1 to the previous value.

In your current enum setup, you have two values set to 1 which may cause unexpected behavior in Typescript/Javascript as it tends to choose the last item with the desired value.

Current code:

enum days{
sun = 1,
mon = 0,
tues
}

VS (a different enum from a functional project of mine)

enum days{
Sun = 0,
Mon,
Tue,
Wed,
Thu,
Fri,
Sat
}

According to the documentation (https://www.typescriptlang.org/docs/handbook/enums.html)

If an enum member does not have an initializer and the preceding one was constant, the value of the current member will be the preceding value plus one. The first element of an enum without an initializer is assigned the value 0.

Answer 4

Your enum structure is quite unique and not following the usual convention. According to the documentation, undefined enums will automatically assign a value by adding 1 to the previous value.

In your current enum setup, you have two values set to 1 which may cause unexpected behavior in Typescript/Javascript as it tends to choose the last item with the desired value.

Current code:

enum days{
sun = 1,
mon = 0,
tues
}

VS (a different enum from a functional project of mine)

enum days{
Sun = 0,
Mon,
Tue,
Wed,
Thu,
Fri,
Sat
}

According to the documentation (https://www.typescriptlang.org/docs/handbook/enums.html)

If an enum member does not have an initializer and the preceding one was constant, the value of the current member will be the preceding value plus one. The first element of an enum without an initializer is assigned the value 0.

Unexpected results observed in enumerators within typescript

Answer №1

Answer №2

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