what does the second agument in a map mean javascript code example

Example 1: javascript map

array.map( item => item.id )

array2.map( item => item.toString() )

array2.map( item => item * 3 )

// this will apply a transformation to all elements of an array
// "" item => something "" is the transformation (function)

Example 2: js map function

const exampleArray = ['aa','bbc','ccdd'];
console.log(exampleArray.map(a => a.length));
//Would print out [2,3,4]