Semantic portal
Map
Let map = new Map();
map.set('1', 'str1'); // a string key
map.set(1, 'num1'); // a numeric key
map.set(true, 'bool1'); // a boolean key
// remember the regular Object? it would convert keys to string
// Map keeps the type, so these two are different:
alert( map.get(1) ); // 'num1'
alert( map.get('1') ); // 'str1'
alert( map.size ); // 3It calls the function for each element of the array and returns the array of results.
Is a collection of keyed data items, just like an Object.
Syntax
Let result = arr.map(function(item, index, array) {
// returns the new value instead of item
})