How Does Array.prototype.slice.call(arguments) Transform Arguments into an Array?

Diving into the Inner Workings of Array.prototype.slice.call(arguments)

Understanding the behavior of Array.prototype.slice.call(arguments) demands an in-depth exploration beyond its surface-level use of converting arguments into a genuine array.

Normally, when slice() is directly invoked on an array, it iterates through the elements of that array. However, using .call() and .apply() offers a unique opportunity to manually define the value of this within a function.

In the case of Array.prototype.slice.call(arguments), an array-like object, possessing numeric .length and indexed properties, is substituted as this. This substitution fools slice() into assuming it's dealing with a genuine array, facilitating its normal operation.

Consider the following example where a plain object, without inherent array properties, is set as this using .call():

var my_object = {
    '0': 'zero',
    '1': 'one',
    '2': 'two',
    '3': 'three',
    '4': 'four',
    length: 5
};

var sliced = Array.prototype.slice.call( my_object, 3 );

Remarkably, slice() acts as expected, yielding the desired result:

['three','four'];

The same mechanism applies when an arguments object is passed as the value for this in Array.prototype.slice.call(arguments). Since arguments have a .length property and an array of numeric indices, slice() proceeds as if operating on a real array, providing a consistent and predictable outcome.

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