I am currently working on incorporating a hashmap/dictionary interface. The progress I have made so far is as follows:
export interface IHash {
[details: string] : string;
}
I am facing difficulties in comprehending the exact meaning of this syntax. If I were to execute var x : IHash = {};, what steps would be involved in adding/accessing the data?
When dealing with a regular JavaScript object:
let myhash: IHash = {};
myhash["somestring"] = "value"; //assign value
let value = myhash["somestring"]; //retrieve value
There are two main purposes of using [indexer: string] : string:
https://i.sstatic.net/LXQ4D.png
If you want to create a dictionary with explicitly typed fields, you can use [key: string]: any;
https://i.sstatic.net/sEZte.png
For example, age must be a number, and name must be a string - both fields are mandatory. Any unspecified field can hold any type of value.
Alternatively, there is the Map class:
let map = new Map<object, string>();
let key = new Object();
map.set(key, "value");
map.get(key); // returns "value"
This feature allows you to use any Object instance as a key, not limited to numbers or strings.
Keep in mind that this functionality is relatively recent, so you might need to include a polyfill if you're targeting older systems.
The easiest and most accurate method involves utilizing the Record type with a declaration of Record<string, string>
const myVariable : Record<string, string> = {
property1: 'value1',
property2: 'value2',
}
let myObject : IHash = {};
myObject['name'] = 'John';
myObject['age'] = 25;
console.log(myObject['name']);
// results in John
console.log(myObject['age']);
// results in 25
If you wish to loop through your dictionary, you can use the following method.
Object.keys(myObject).forEach((key) => {console.log(myObject[key])});
The Object.keys function retrieves all properties of an object, making it suitable for returning values from dictionary-like objects.
You mentioned a hashmap in your query; the definition provided is for a dictionary-style interface where keys are unique but not values.
To treat it like a hashset, assign the same value to both key and value fields.
If you want unique keys with potentially different values, verify if the key exists before adding it.
let newValue = 'apple';
if(!myObject[newValue])
myObject[newValue] = newValue;
Alternatively, create a custom class to serve as a hashset.
Class MyHashSet{
private var keys: IHash = {};
private var values: string[] = [];
public addKey(key: string){
if(!keys[key]){
values.push(key);
keys[key] = key;
}
}
public getValues(){
// Copying the array prevents accidental alterations by users
return values.slice();
}
}
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