Object with another's object's property as a key

Question

I have an object like this: var myObj = {action1:0, action2:1, action3:2};

Test function gets values from this list as parameters and to simplify unit-testing I want

Answer 1

In ES5 and earlier, you have to create that object with a series of statements:

var dictObj = {};
dictObj[myObj.action1] = "action1";
dictObj[myObj.action2] = "action2";
dictObj[myObj.action3] = "action3";

As of ES2015 (aka "ES6"), you can do it with computed property names in the object initializer instead:

let dictObj = {
    [myObj.action1]: "action1",
    [myObj.action2]: "action2",
    [myObj.action3]: "action3"
};

You can use any expression within the [] to create the property name; in this case it's just a simple property lookup.

In both cases, note that there's no live relationship; if you change myObj.action1 to 42 later, after doing the above, it doesn't have any effect on the property name in dictObj.