javascript: how to get index of an object in an associative array?

Question

var associativeArray = [];

associativeArray['key1'] = 'value1';
associativeArray['key2'] = 'value2';
associativeArray['key3'] = 'value3';
associativeArray['key4'] = 'value4';
associativeArray['key5'] = 'value5';

var key = null;
for(key in associativeArray)
{
    console.log("associativeArray[" + key + "]: " +  associativeArray[key]);        
}

key = 'key3';

var obj = associativeArray[key];        

// gives index = -1 in both cases why?
var index = associativeArray.indexOf(obj); 
// var index = associativeArray.indexOf(key);  

console.log("obj: " + obj + ", index: " + index);   

---

The above program prints index: -1, why? Is there any better way to get index of an object in an associative array without using loops?

What if I want to delete 'key3' from this array? the splice function takes first parameter as index which must be an integer.

Answer 1

indexOf only works with pure Javascript arrays, ie those with integer indexes. Your "array" is actually an object and should be declared as such

var associativeArray = {}

There's no built-in indexOf for objects, but it's easy to write.

var associativeArray = {}

associativeArray['key1'] = 'value1';
associativeArray['key2'] = 'value2';
associativeArray['key3'] = 'value3';
associativeArray['key4'] = 'value4';
associativeArray['key5'] = 'value5';

var value = 'value3';
for(var key in associativeArray)
{
    if(associativeArray[key]==value)
         console.log(key);
}

Without loops (assuming a modern browser):

foundKeys = Object.keys(associativeArray).filter(function(key) {
    return associativeArray[key] == value;
})

returns an array of keys that contain the given value.

Answer 2

If you don't use jQuery, you could extend the prototype of Object doing this:

// Returns the index of the value if it exists, or undefined if not
Object.defineProperty(Object.prototype, "associativeIndexOf", { 
    value: function(value) {
        for (var key in this) if (this[key] == value) return key;
        return undefined;
    }
});

Using this way instead of the common Object.prototype.associativeIndexOf = ... will work with jQuery if you use it.

And then you could use it like this:

var myArray = {...};
var index = myArray.associativeIndexOf(value);

It will also work with normal arrays: [...] , so you could use it instead of indexOf too.

Remember to use the triple-character operators to check if it's undefined:

index === undefined // to check the value/index exists    
index !== undefined // to check the value/index does not exist

Of course you could change the name of the function if you prefer to for example keyOf , and remember not to declare any variable called 'undefined'.

Answer 3

let elementIndex = -1;

array.forEach((element, index, array) => {
   if (element["key"] == "someValue") {
      elementIndex = index;
   }
});

TypeScript Style:

let elementIndex = -1;

this.array.forEach((element, index, array) => {
   if (element.key. == "someValue") {
      elementIndex = index;
   }
});