Index of array based on value

[Shadowfax]

Is there any inbuilt method to get the index of a \n array by its value (in JSX). It seems that indexOf doesn't work here as in javascript..

[Vamitul]

nope!

i use this:

Array.prototype.findIndex = function (value)
{
          var ctr = "";
          for (var i = 0; i < this.length; i++)
          {
                    // use === to check for Matches. ie., identical (===), ;
                    if (this == value)
                    {
                              return i;
                    }
          }
          return ctr;
};

don't know from who i got this snippet, but lots and lots of thanks

[Harbs.]

JSX is based on an older version of ECMAScript. indexOf did not used to exist for Arrays.

Here's an implementation that's equivalent to the javascript version:

Array.prototype.indexOf = function (elem, fromIndex){
    fromIndex = fromIndex || 0;
    for(var i = fromIndex; i < this.length; i++){
        if(this == elem){
            return i;
        }
    }
    return -1;
}

There's a problem with Vamitul's version in that it returns a blank string if the index is not found, but it returns a number if it is. That makes it difficult to determine if the index is found or not. With the standard implementation you test for index < 0 to determine if the element is not found.

Harbs

[Harbs.]

Here's a more robust version which supports negative indices as well:

Array.prototype.indexOf = function (elem, fromIndex){
    fromIndex = Number(fromIndex) || 0;
    var len = this.length;
    if (fromIndex < 0){
        fromIndex += len;
    }
    for(var i=fromIndex;i<this.length;i++){
        if(this == elem){
            return i;
        }
    }
    return -1;
}

[Harbs. · Accepted solution]

FWIW, here's the implementation recommended by Mozilla (which has more robust error checking) :

if (!Array.prototype.indexOf) {
    Array.prototype.indexOf = function (searchElement /*, fromIndex */ ) {  
        "use strict";
        if (this == null) {
            throw new TypeError();
        }
        var t = Object(this);
        var len = t.length >>> 0;
        if (len === 0) {
            return -1;
        }
        var n = 0;
        if (arguments.length > 0) {
            n = Number(arguments[1]);
            if (n != n) { // shortcut for verifying if it's NaN
                n = 0;
            } else if (n != 0 && n != Infinity && n != -Infinity) {
                n = (n > 0 || -1) * Math.floor(Math.abs(n));
            }
        }
        if (n >= len) {
            return -1;
        }
        var k = n >= 0 ? n : Math.max(len - Math.abs(n), 0);
        for (; k < len; k++) {
            if (k in t && t === searchElement) {
                return k;
            }
        }
        return -1;
    }
}

[Shadowfax]

thnx a lt for wonderful guide