Collections in TypeScript

 Typescript is providing with collections:

 1.Map collection
 2.Weak Map collection
 3.Set collection

 4 Weak set Collection

Map collection:

*Map is a collection of key and value pairs, key should be an unique
*key and value can be of any type

Syntax:
let <mapobject>=new Map();

Methods

 1.Set(key, value)-It will add | modify an element of map collection, it will
                  return map object

    key is not existing-->adding
    key is existing    -->modifying

 2.get(key)        It will return a value based on key
 3.delete(key)    It will delete an element based on key
 4.has(key)        It will verify whether element based on key is present or not, it
                         will return true | false
                        
                        true--existing
                        false--not existing

 5.size               It will return collection count
 6.keys()           It will return keys collection
 7.values()         It will return values collection
 8.entries()        It will return key and value collection


Example






















Output

Map (4) {1 => "angular", 2 => "reactjs", 3 => "nodejs", 4 => "azure"} 
Map (4) {1 => "angular17", 2 => "reactjs", 3 => "nodejs", 4 => "azure"} 
false 
1 
2 
3 
"angular17" 
"reactjs" 
"nodejs" 
1,  "angular17" 
2,  "reactjs" 
3,  "nodejs" 


WeakMap:

Weak map is a collection of key and value pairs, 

key should be an unique

key should be an object and value can be of any type.

Setting key to null, will remove corresponding element automatically from weak map collection, this will not happen with map collection

Methods[same as Map collection]:
 1.set(key,value)
 2.get(key)
 3.delete(key)

Example:

let weakmap=new WeakMap();
let user1={name:"charan"};//object[key]
let msgs1=["hi","how r u"];//value

let user2:string | null
user2={name:"raju"};
let msgs2=["fine","thank u"];

weakmap.set(user1,msgs1);
weakmap.set(user2,msgs2);
console.log(weakmap.get(user1));
console.log(weakmap.get(user2));

Output

["hi", "how r u"] 
["fine", "thank u"] 

Set:
----
Set is a collection of unique values, value can be of any type.
Set is similar to an array, but array allows duplicate values, where as set allows unique value

Array will have restricted size, where as set will not have size restriction

Methods:
 1.add(value)--it will add an element into set collection
 2.delete(value)
 3.values()--it will return values collection

Example

let set=new Set();
set.add("hyd").add("bang").add("chennai").add("noida");
console.log(set);
set.add("hyd");//it will not add
console.log(set);
let arr=Array.from(set);//it will create an array based on set
arr.push("hyd");//it will add an element to an array,it will not reflect on set
console.log(arr);
console.log(set);

Output

Set (4) {"hyd", "bang", "chennai", "noida"} 
Set (4) {"hyd", "bang", "chennai", "noida"} 
["hyd", "bang", "chennai", "noida", "hyd"] 
Set (4) {"hyd", "bang", "chennai", "noida"} 


Note
-----
Collections are provided with generic to specify particular datatype

   map()[non generic]                map<type,type>()[generic] 

   set()[non generic]                  set<type>() [generic]

   let set1=new Set<number>(); [set can accept only
                                                 unique numbers]

WeakSet:
--------
Weak Set is a collection of unique values, value should be an object

Setting value to null, will remove corresponding element automatically from weak set collection.