CODEWITHSUNDEEP
javascriptprototypeprototype-programming
Jinxal
Jinxal

Reputation: 51

Object prototyping

In my javascript code I often need to check if an expression in some enumerable list like this:

if ((a == 'value1') || (a == 'value2') || (a == 'value3')) { ... do smth ... }

I can write something like this:

if (['value1', 'value2', 'value3', 'value4'].indexOf ( a ) ) { ... do smth ... }

but I think it's unreadable.

I add property in_arr for Object.prototype:

Object.defineProperty(Object.prototype, 'in_arr', {
    value : function(arr) {
                for (var i=0; i<arr.length; i++) {
                    if ( arr[i] == this.valueOf() ) {
                        return true;
                    }
                }
                return false;
             },
    enumerable: false
})

And now I can write like this:

if (a.in_arr([ 'value1', 'value2', 'value3', 'value4' ]) { ... do smth ... }

I think, it's looks good. But I want to ask: Is it safe to change Object.prototype like this? And what about perfomance?

Upvotes: 0

Views: 90

Answers (4)

A. Mat&#237;as Quezada
A. Mat&#237;as Quezada

Reputation: 1906

It's not recomended to extend Object.prototype, this will lead to strange behaviours and there is no need to do it one way if there is a less dangerous one like a simple function.

in_array(obj, [ 'a', 'b', 'c' ]);

You can even create a utils object

utils.in_array(obj, [ 'a', 'b', 'c' ]);

Once I've said that...

This looks very similar to Extending Object.prototype JavaScript and I totally agree with Alex Wayne:

I think it's fine if it works in your target environment.

Also I think prototype extension paranoia is overblown. As long as you use hasOwnProperty() like a good developer that it's all fine. Worst case, you overload that property elsewhere and lose the method. But that's your own fault if you do that.

Upvotes: 0

Vitalii Del Vorobioff
Vitalii Del Vorobioff

Reputation: 525

Wrong way to change system objects like Array, Object etc. Because conflicts may occur if anyone do such changes

Upvotes: 0

raina77ow
raina77ow

Reputation: 106365

Create an enumeration hash, like this:

var enumHash = {
  value1: true,
  value2: true,
  value3: true
  // actually it doesn't matter which value to assign: 
  // even undefined will do, as you check the existence of a property, not its value
};

... then just check the existence of a property:

if (someValue in enumHash) { ... }

That'll be both faster than Array.indexOf and more readable.

Upvotes: 3

Romko
Romko

Reputation: 1798

you can just use Array.prototype.indexOf(el)

[ 'value1', 'value2', 'value3', 'value4' ].indexOf(a.valueOf()) !== -1

Upvotes: -2

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