How to access string using prototype

Question

I am trying to write a function which returns the middle character of a string. I want it to work like the code below :

"123456789".midChar(); // Returns 5
"hello".midChar(); // returns 1
"test".midChar(); // returns e

I want to know how can I access the string if the function takes no parameters? How can I refer to the strings inside of the function to be able to manipulate it? For example "123456789"

What have I done before asking this question?

I read about prototypes and understood how I can add methods to the array and string prototype. I tried to find the implementation of String.prototype.charAt() and several other ones to understand how it's built, but couldn't find one. All i was able to find is Reduce, ForEach and several other Array methods, but that wasn't very helpful to my case.

Inside the prototype, the string will be set as the context, so you can access it via this. — VLAZ
– VLAZ, Commented Oct 19, 2018 at 14:59
Why does it have to be a method on String rather than a plain function that takes a string as an argument? — Stefano
– Stefano, Commented Oct 19, 2018 at 15:01
Just for educational purposes, i want to know how prototypes work in depth, so im trying to build this. — Christian Benjamin
– Christian Benjamin, Commented Oct 19, 2018 at 15:02

wang · Accepted Answer · 2018-10-19 15:14:21Z

2

use this inside midChar function to access the string.

String.prototype.midChar = function() {
  var mid = parseInt((this.length - 1) / 2)
  return this.substring(mid, mid+1);
}

console.log("123456789".midChar())
console.log("hello".midChar())
console.log("test".midChar())

answered Oct 19, 2018 at 15:14

wang

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1 Comment

Christian Benjamin Over a year ago

Is there a reason why you are returning "this.substring(mid, mid+1)" instead of doing "return this[mid];" ?

Ele · Accepted Answer · 2018-10-19 15:05:18Z

1

String.prototype.midChar= function () {
    console.log(String(this)); // 'this' is the string representation.
    console.log(this.substring(5));
    console.log(this);
};

"EleFromStack".midChar();

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answered Oct 19, 2018 at 15:05

Ele

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Comments

Pim · Accepted Answer · 2018-10-19 15:02:05Z

0

extend the prototype like this

String.prototype.midChar= function () {
    //put yout function body here..
    //i.e.
    //var firstchar = this.charAt(0)
};

that should do it!

edited Oct 19, 2018 at 15:02

answered Oct 19, 2018 at 15:00

Pim

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1 Comment

Christian Benjamin Over a year ago

Yes, that wasnt my question. My question is how i can access the string inside of this function

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