Can I create a class [] operator in Typescript

Question

Is there a way to override the [] operation in typescript? We use 1.4 so we're fine with a solution that requires 1.4.

Update: I was horribly unclear in my initial question. What I meant was can I add that as an operator to a class. In my class I presently have a method:

public get(index : number) : LinkedListNode<t> {

    if (this._first === null || (index >= this._count)) {
        return null;
    }
    var node = this._first;
    while (index-- > 0) {
        node = node._next;
    }
    return node;
}

I would prefer to be able to call data[5] instead of data.get(5).

Is there a way to do this?

thanks & sorry for the incredibly inaccurate initial question.

Answer 1

Update

In response to your update to your question, no it's not possible to overload the index operator for a class—you can't do data[5] instead of data.get(5).

In my opinion, the reason this has not been implemented is because JavaScript allows accessing an object's properties using brackets and that creates some ambiguity. For example, if data.myProperty is a property that exists and data['myProperty'] is called, then it would be difficult to decide if it should return the myProperty property or if the string 'myProperty' should be passed to the index overload.

Original Answer

It's not possible to change the result of:

var a = [];

Imagine the problems that could occur if people were allowed to change that behaviour? Library A could define it one way and then Library B could overwrite that with its own behaviour... meaning Library B now uses Library A's [] behaviour.

What you can do is add methods to Array's prototype:

interface Array {
    log: () => void;
}

Array.prototype.log = function() {
    console.log(JSON.stringify(this));
};

Then use:

var a = [];
a.log();

However, doing this is extremely not recommended! You shouldn't be modifying objects you don't own because it can lead to unforeseen problems. The reason not to do this is similar to why changing []'s behaviour would lead to problems:

1. Library A defines a log method.
2. Library B defines a log method that works differently.
3. Now the log method for Library A won't work as expected because it's using Library B's method.

Recommendation

I would suggest creating your own implementation of array:

class MyArray<T> implements Array<T> {
    private _underlyingArray : Array<T> = [];

    // implement methods for Array here

    log() {
        console.log(JSON.stringify(this._underlyingArray));
    }
}

Or create a helper class:

class ArrayHelper {
    static log<T>(a: Array<T>) {
        console.log(JSON.stringify(a));
    }
}

Answer 2

Operators cannot be overloaded in JavaScript / TypeScript.

With ECMAScript 6, you'll be able to use iterators. TypeScript 1.5 adds the support of Symbols with the target ES6. But iterators are not available in TypeScript with ES5/3 as target.

Answer 3

usually, arrays are a list of variables/values(maybe character/integer/float)

instead of this, you can manually use objects.. Example:

var objtest = {first: "one", second:"two"}; then you can use each element this way:

objtest.first; -- outputs one objtest.second; -- outputs two if you want you can use it as each variable..

Example: var first = "one"; var second = "two" ;

I prefer using the first way.

I hope it helped.