Problem to extend array

Question

i have a problem. I have written a code for extend Array Element, and works fine, but when i iterate over array this show extended functions. I don't know how stop this. There is the code...

Array.prototype.remove  = function(e)   {var i = this.inArray(e);if(i != -1) this.splice(i, 1);return this;};
Array.prototype.add     = function(e)   {this.push(e); return e;};
Array.prototype.inArray = function(v)   {for(i in this) if(v==this[i])return i;return false;};
Array.prototype.toggle  = function(v)   {this.inArray(v) ? this.remove(v) : this.add(v);return this;};

So when i tried this...

var arr = [1,2,3,4,5];
for(i in arr)
document.write(arr[i]);

this print array values and functions extended. somebody can help me? I can't change the code "for(x in y)" because is many times in many files.

You're trying to iterate over the values in the array, but it's iterating over your custom functions as well? — sdleihssirhc
– sdleihssirhc, Commented Aug 15, 2011 at 23:42
You should not use for..in with arrays because the order of enumeration is implementation dependent. Most browsers will return numeric keys first in lowest to highest order, but IE will return keys in the order they are added. So you will get lowest to highest only if that is the order in which they were added. e.g. `var i=2, a=[], p;while(i--)a[i] = i;for(p in a) alert(p);' shows 0, 1 in most browsers but 1, 0 in IE. — RobG
– RobG, Commented Aug 15, 2011 at 23:56
"I can't change the code..." Sure you can, and you should. The cost of writing faulty code is fixing faulty code. — user113716
– user113716, Commented Aug 15, 2011 at 23:58
[Waves hand] "You will fix the faulty JavaScript." OP replies: "I will fix the faulty JavaScript." — user113716
– user113716, Commented Aug 16, 2011 at 0:02

sciritai · Accepted Answer · 2011-08-15 23:55:16Z

2

Couple of things to read that will explain the situation

https://developer.mozilla.org/en/JavaScript/Reference/Statements/for...in

https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Object/hasOwnProperty

Use .forEach() when iterating over an array. It's pretty well supported, including Mobile Safari and Android, https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/forEach

edited Aug 15, 2011 at 23:55

answered Aug 15, 2011 at 23:46

sciritai

3,7481 gold badge19 silver badges22 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

alex Over a year ago

forEach() isn't widely supported yet, but it is a good option if your target platforms support it.

alex Over a year ago

It's pretty well supported The only IE that supports it is is IE9. For most public facing websites that is a bit of an issue (unless you monkey patch it, the MDN docs have a good example).

alex · Accepted Answer · 2011-08-15 23:45:34Z

1

If you must modify the Array prototype, you must use hasOwnProperty() otherwise it will pick up properties up the prototype chain.

var arr = [1,2,3,4,5];
for(var i in arr) {
    if (arr.hasOwnProperty(i)) {
        document.write(arr[i])
    }
}

You said, however, you don't want to change your for (in) loops. Why don't you have an Array utility object? Or just use normal for loops? These are Arrays right? for (in) is for iterating over Object properties.

answered Aug 15, 2011 at 23:45

alex

492k205 gold badges890 silver badges992 bronze badges

Comments

cdhowie · Accepted Answer · 2011-08-15 23:43:12Z

0

for ... in loops through object properties in JavaScript, not array elements. The for ... in loops are simply the wrong way to do this. You've said that you can't change them, but using this syntax to enumerate the contents of arrays is not a recommended practice in JavaScript, for the reason you have just discovered.

You are going to have to rewrite the for ... in loops sooner or later.

answered Aug 15, 2011 at 23:43

cdhowie

172k25 gold badges303 silver badges324 bronze badges

2 Comments

RobG Over a year ago

Arrays are objects, for..in will loop over all array properties, including the ones with numeric names.

cdhowie Over a year ago

Exactly. Which means that using for ... in as though it were foreach from other languages is wrong.

kennebec · Accepted Answer · 2011-08-16 04:22:25Z

0

Iterate through the array's indexes.-

var A=[1,2,3,4,5];

Array.peototype.omega=function(replacer){
  var L= this.length;
  if(L)--L;
  if(replacer!=undefined)this[L]=replacer;
  return this[L]
}

for(var i=0,L=A.length; i<L; i++){
//do something to A[i]
}

answered Aug 16, 2011 at 4:22

kennebec

105k32 gold badges109 silver badges127 bronze badges

Collectives™ on Stack Overflow

Problem to extend array

4 Answers 4

2 Comments

Comments

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

2 Comments

Comments

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related