Javascript: Array vs Hash as array

/* define */
var array = [];

/* add elements */

// by index
array[0] = 'foo';
array[1] = 'bar';

// add element at start
array.unshift('foo', 'bar'); // add two elements

// add element at the end
array.push('foo', 'bar'); // add two elements

/* delete elements */

// delete 1 element from index 0 (delete element at index 0)
array.splice(0, 1) // note that delete array[0] will set that element to undefined but array length not changed

// delete element at start
array.shift();

// delete element at the end
array.pop();


/* length */

array.length
// note if we set array[1000] = 'some thing' then array.length will be 999
// array length don't care about how much item we add but about bigest index we add.

/* loop */

for(var i = 0; i < array.length; i ++) {
    // do some thing with array[i]
}
// or
for(var i in array) {
    if(!array.hasOwnProperty(i)){ continue; }

    // do some thing with array[i]
}
// or
array.forEach(function(value, index){
    // do some thing with value and index
});
        

/* define */
var hash = {};

/* add elements */

// number as key
hash[1] = 'foo';

// string as key
hash['bar'] = 'foo';
// or
hash.bar = 'foo';



/* delete elements */

delete hash[1]; // delete hash.1 will give error

delete hash['bar']
// or
delete hash.bar





/* length */

// hash seem not have length method but we can use this
Object.keys(hash).length


/* loop */

for(var key in hash) {
    if(!hash.hasOwnProperty(key)){ continue; }

    // do some thing with hash[key] (not hash.key)
}