Syntax
array.map(function(currentValue, index, arr), thisValue)
Parameter Values
Parameter	Description
function(currentValue, index, arr)	Required. A function to be run for each element in the array.
Function arguments:
Argument	Description
currentValue	Required. The value of the current element
index	Optional. The array index of the current element
arr	Optional. The array object the current element belongs to
thisValue	Optional. A value to be passed to the function to be used as its "this" value.
If this parameter is empty, the value "undefined" will be passed as its "this" value

examples

service.currencyList.map(each({value:each.currencySymbol,displayValue:each.currencySymbol}))

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const persons = [
  {firstname : "Malcom", lastname: "Reynolds"},
  {firstname : "Kaylee", lastname: "Frye"},
  {firstname : "Jayne", lastname: "Cobb"}
];

persons.map(getFullName);

function getFullName(item) {
  return [item.firstname,item.lastname].join(" ");
}