How to check if a username is taken, by checking against a JavaScript array.

Question

var y=document.forms["form"]["user"].value
    if (y==null || y=="" )
        {
            alert("Username cannot be Blank");
            return false;
        };

var x = new Array();
    x[0] = "bill";  
    x[1] = "ted";   
    x[2] = "jim";   
    for ( keyVar in x ) 
        {
            if (x==y)
            {
                alert("Username Taken");
                return false;
            };

        };

How do I compare a variable to that in a JavaScript array, I managed to make the example above, but the second part, the bit I need, doesn't work. any ideas ?

jAndy · Accepted Answer · 2011-12-02 13:35:08Z

4

You can simply check an array with the Array.prototype.indexOf method.

var x = [ 'bill', 'ted', 'jim' ],
    y = 'ted';

if( x.indexOf( y ) > -1 ) {
    alert('Username Taken');
    return false;
}

answered Dec 2, 2011 at 13:35

jAndy

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3 Comments

Nicola Peluchetti Over a year ago

I think that indexOf is much slower than checking if the property of an object is true (and this get more relevant as the array grows in size)

John Strickler Over a year ago

@Nicola this is probably the most straight forward answer since the OP wants to search against an array. If the array was sorted then we could use a binary search. Otherwise, using an object would probably yield better results... (keys/values, TRIE etc)

jAndy Over a year ago

@NicolaPeluchetti: the array would need to become really huge before performance becomes an issue. However, ES.next will solve all the problems, weakmaps are coming :)

Nicola Peluchetti · Accepted Answer · 2011-12-02 13:34:52Z

3

You should use an object instead:

var y = document.forms["form"]["user"].value;
if (y == null || y == "") {
    alert("Username cannot be Blank");
    return false;
};

var x = {};
x["bill"] = true;
x["ted"] = true;
x["jim"] = true;
if (x[y] === true) {
    alert("Username Taken");
    return false;
}

answered Dec 2, 2011 at 13:34

Nicola Peluchetti

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Comments

Amadeus · Accepted Answer · 2011-12-02 13:37:19Z

3

You can do this quite simply with jQuery

The list of the array values

var x = new Array();
x[0] = "bill";  
x[1] = "ted";   
x[2] = "jim";

then

 if(jQuery.inArray("John", arr) == -1){
     alert("Username Taken");
 }

answered Dec 2, 2011 at 13:37

Amadeus

1898 bronze badges

1 Comment

Nicola Peluchetti Over a year ago

There is no jQuery involved here i think

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