What is the reason behind the array slice method's ability to convert nodelists or arguments into arrays in JavaScript?

I am familiar with using the following:

Array.prototype.slice.call(document.querySelectorAll('a'))

to convert Nodelist data type to an array without specifying a parameter. However, I came across information from the W3CSchool regarding the usage of slice, which mentions that the first parameter start is required:

start Required. An integer that specifies where to start the selection (The first element has an index of 0). Use negative numbers to select from the end of an array

So, is it acceptable to not specify a parameter and still call that method successfully? How does this work?

javascriptarraysslice

Answer №1

Join me in a game of following the trail of breadcrumbs

According to the es5 specification,

  1. Array.prototype.slice(start, end)

    Let's define relativeStart as ToInteger(start)

  2. ToInteger

    1. Assign the value of calling ToNumber on the input argument to number

  3. ToNumber

    Undefined transforms into NaN

  4. Go back and look at ToInteger

    2. If number is NaN, return +0.

Therefore, even though it may not be explicitly mentioned as optional, if start is undefined, it is treated as 0.

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