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Javascript – How to avoid inherited methods in call by super constructor keyword

I have extended class from Map:

class ModifiedMap extends Map {
  constructor(arg) {
    super(arg);
  }
  set(key, value) {
    console.log("doing some work here")
  }
}

And if I try to create ModifiedMap, I see "doing some work here" printing n times (depends on iterator).

new ModifiedMap([["a", "apple"],["b", "orange"],["c", "banana"]])

How can I avoid using my subclass’s set method in the internal algorithm of constructing Map? Sure I could rename from set to any name, but I want to know is it possible use the same name?

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2

Answers


  1. 0

    You could use a flag to tell your subclass set whether the instance construction is complete, then check that flag in set. If the flag isn’t set, pass the call on to super.set:

    class ModifiedMap extends Map {
    constructor(arg) {
        super(arg);
        this.ready = true;
    }
    set(key, value) {
        if (this.ready) {
            console.log("doing some work here");
        } else {
            return super.set(key, value);
        }
    }
}

console.log("Constructing...");
const map = new ModifiedMap([["a", "apple"],["b", "orange"],["c", "banana"]]);
console.log("Done constructing, adding an entry");
map.set("x", "y");

    That said, it seems fairly odd to bypass your subclass’s customized set only during construction. A separate method specific to the subclass may be a better idea.

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  2. 0

    A variation of @T.J.Crowder’s solution is to add the flag to the overriden method. Internal calls will not provide this flag, but your custom calls can pass it conditionally.

    class ModifiedMap extends Map {
    set(key, value, dowork) {
        if (dowork !== undefined) {
            console.log("doing some work here");
        } else {
            return super.set(key, value);
        }
    }
}

console.log("Constructing...");
const map = new ModifiedMap([["a", "apple"],["b", "orange"],["c", "banana"]]);
console.log("Done constructing, adding an entry");
map.set("x", "y", true);  // <-- pass something when calling set
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