CODEWITHSUNDEEP
javascript
robin
robin

Reputation: 1925

Issue with my var getting undefined

I am trying to create a reverse function to the String type in javascript. My code is like 

String.prototype.reverse = function () {
    var s = "";
    for(var i=this.length;i>=0;i--){
            s+=this[i];
    }
    return s;
}

When I try to use it on for example like "test".reverse();

instead of giving "tset" it's giving "undefinedtset"

I am setting the variable like var s = ""; inside the function, still undefined is coming. Why is it so?

Upvotes: 0

Views: 65

Answers (3)

Chin Leung
Chin Leung

Reputation: 14941

The reason why your code isn't working has been answered by the others already, but if you want a shorter version of the reverse, you can do it like this:

String.prototype.reverse = function(){
  return this.split('').reverse().join('');
}

console.log('Hello World'.reverse())

Upvotes: 2

hsz
hsz

Reputation: 152284

this.length gives you 4 (4 letters in test word) and you start iterating from 4 to 0.

The problem is that nothing exists under 4 index (your letters are stored in 0-3 positions).

Try with:

for (var i = this.length - 1; i >= 0; i--) {
    s += this[i];
}

Upvotes: 3

Zenoo
Zenoo

Reputation: 12880

You just need to change var i=this.length to var i=this.length-1, because an array starts at position 0 :

String.prototype.reverse = function () {
    var s = "";
    for(var i=this.length-1;i>=0;i--){
            s+=this[i];
    }
    return s;
}

Upvotes: 4

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