Get Enum Element Name in Typescript

/ February 17, 2018/ Typescript

(Last Updated On: February 18, 2018) Sometimes while debugging a Typescript base project we need to check if a parameter has the correct Enum type. Usually we have something like

let myVariable = myEnum.myType
console.log(`myVariale is ${myVariable}`);

but that will print just a number (the index position of the Enum). If we need to print the Enum value name we can see in the transpiled version of an Enum to get some help.

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Typescript Source

enum myEnum{
    Up,
    Down,
    Left,
    Right,
    myType
}
console.log(myEnum.myType); // outputs 4

Transpiled Javascript

var myEnum;

(function (myEnum) {
    myEnum[myEnum["Up"] = 0] = "Up";
    myEnum[myEnum["Down"] = 1] = "Down";
    myEnum[myEnum["Left"] = 2] = "Left";
    myEnum[myEnum["Right"] = 3] = "Right";
    myEnum[myEnum["myType"] = 4] = "myType";
})(myEnum || (myEnum = {}));

console.log(myEnum.myType);

Did you see it? myEnum is just an Object with numerical and string keys. If we simplify it more we have:

Transpiled and Simplified Javascript

var myEnum;
(function (myEnum) {
  
    myEnum["Up"] = 0;
    myEnum[0] = "Up";
    
    myEnum["Down"] = 1;
    myEnum[1] = "Down";
    
    myEnum["Left"] = 2;
    myEnum[2] = "Left";
    
    myEnum["Right"] = 3;
    myEnum[3] = "Right";
    
    myEnum["myType"] = 4;
    myEnum[4] = "myType";
    
})(myEnum || (myEnum = {}));
console.log(myEnum.myType) // Outputs 4;

Now is really clear, each Enum.someValue has its numerical pair and we can use this numerical pair to get the name in this way:

enum myEnum{
    Up,
    Down,
    Left,
    Right,
    myType
}
console.log(myEnum.myType); // outputs 4

console.log(myEnum[myEnum.myType]); //outputs myType
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