Merge pull request #3 from rawpixel-vincent/add-value-method

add `value(T):T` method to get a constant from the list

README.md

@@ -41,6 +41,9 @@ v.withSuffix('.suffix') => SL<"foo.suffix" | "bar.suffix">
 
 v.concat('zing', 'boom', stringList('zig', 'zag')) => SL<"foo" | "bar" | "zing" | "boom" | "zig" | "zag">;
 
+v.value('foo') => 'foo';
+
+v.value('not') => throws;
 ```
 
 ## Installation
@@ -80,6 +83,13 @@ const bothWay = list.withPrefix('data.').withSuffix('.ext');
 let val;
 list.includes(val); // No type error just boolean result.
 // list implements similar fix for indexOf, lastIndexOf, filter, some, every, findIndex and find methods.
+
+// Get a copy of the underlying array -> string[]
+const arr = list.mutable(); // => ["foo", "bar"]
+
+// access a value in the list
+list.value('foo'); // 'foo'
+list.value('n'); // throws error
 ```
 
 #### list.concat(...(string|StringList)[])

StringLiteralList.d.ts

@@ -18,6 +18,7 @@ export interface IStringList<T extends unknown>
   withSuffix<P extends string>(
     suffix: P,
   ): IStringList<sl.utils.StringConcat<T extends string ? T : string, P>>;
+  value<V extends T & string>(val: V): V extends T ? T : never;
   mutable(): string[];
 
   // Implemented methods to return the frozen array, typed as IStringList.

StringLiteralList.js

@@ -25,6 +25,13 @@ export class SL extends Array {
     return Object.freeze(new SL(...super.map((e) => `${e}${suffix}`)));
   }
 
+  value(value) {
+    if (this.includes(value)) {
+      return value;
+    }
+    throw new Error(`Invalid value ${value}`);
+  }
+
   // Get the native array
   mutable() {
     return Array.from(this);

package.json

@@ -1,6 +1,6 @@
 {
   "name": "string-literal-list",
-  "version": "1.4.1",
+  "version": "1.5.0",
   "description": "an array for string literal",
   "main": "stringList.js",
   "types": "stringList.d.ts",

stringList.test.js

@@ -32,8 +32,11 @@ const testExpectedArrayValues = (st, list, ...values) => {
     st.ok(list.findIndex((v) => v === value) === i);
     st.ok(list.some((v) => v === value) === true);
     st.ok(list.every((v) => v === value) === (list.length === 1));
+    st.ok(list.value(value) === value);
   }
 
+  st.throws(() => list.value(`${Math.random() * 100000}!`));
+
   st.notOk(list.includes(null));
   st.ok(list.at(values.length) === undefined);
 };
@@ -283,3 +286,5 @@ t.test('stringList mutable', (t) => {
   });
   t.end();
 });
+
+stringList('d').value('d');

types.d.ts

@@ -28,7 +28,8 @@ export namespace sl {
       | 'withPrefix'
       | 'withSuffix'
       | 'toReversed'
-      | 'toSorted';
+      | 'toSorted'
+      | 'value';
 
     /**
      * @description