JavaScript - Difference between Array and Array-like object

Question

I have been coming across the term \"Array-Like Object\" a lot in JavaScript. What is it? What\'s the difference between it and a normal array? What\'s the difference betwee

Answer 1

The famous HTMLCollection (documentation) and the arguments (documentation) are array-like object that automatically created.

Some quick array-like (e.g HTMLCollection) differences between real array examples:

var realArray = ['value1', 'value2'];
var arrayLike = document.forms; 

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Similarities:

The length getter is the same:

arrayLike.length; // returns 2;
realArray.length; // returns 2; //there are 2 forms in the DOM.

The indexed getter is the same:

arrayLike[0]; // returns an element.
realArray[0]; // returns an element. ('value')

They are both objects:

typeof arrayLike; // returns "object"
typeof realArray; // returns "object"

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Differences:

In array-like the join(), concat(), includes() etc, methods are not a functions:

arrayLike.join(", "); // returns Uncaught TypeError: arrayLike.join is not a function (also relevant to `concat()`, `includes()` etc.)
realArray.join(", "); // returns "value1, value2"

The array like is not really an array:

Array.isArray(arrayLike); //returns "false"
Array.isArray(realArray); //returns "true"

In array like you can't set the length property:

arrayLike.length = 1;
arrayLike.length; //return 2; //there are 2 forms in the DOM.
realArray.length = 1;
realArray.length; //return 1;