✨ Handling model name conflict error and updated Doc

Handled the case where a pre defined model model name conflict with a custom one and updated doc

Author: shadokan87

README.md

@@ -177,7 +177,7 @@ main()
 
 Token.js allows you to extend the predefined model list using the `extendModelList` method. Here are some example scenarios where this is useful:
 1. Adding AWS Bedrock models with regional prefixes like `us.anthropic.claude-3-sonnet`
-2. Supporting new model versions like `gpt-4-1106-preview` before they're added to the predefined list
+2. Supporting new model versions before they're added to the predefined list
 3. Using custom model deployments with unique names
 4. Adding experimental or beta models during testing
 
@@ -207,7 +207,7 @@ const result = await tokenjs.chat.completions.create({
 });
 ```
 
-Note: When using extended models, you might need to use type casting (`as any`) for the model parameter.
+Note: When using extended models, type casting (`as any`) is required
 
 The `featureSupport` parameter can be either:
 - A string matching an existing model name from the same provider to copy its feature support

src/index.ts

@@ -1,4 +1,5 @@
 import { LLMChat, LLMProvider } from './chat/index.js'
+import { InputError } from './handlers/types.js'
 import { models } from './models.js'
 import { ConfigOptions } from './userTypes/index.js'
 export * from './userTypes/index.js'
@@ -76,11 +77,6 @@ export class TokenJS implements TokenJSInterface {
 
   /**
    * Extends the predefined model list by adding a new model with specified features.
-   * This is useful for:
-   * 1. Adding AWS Bedrock models with regional prefixes like `us.anthropic.claude-3-sonnet`
-   * 2. Supporting new model versions like `gpt-4-1106-preview` before they're added to the predefined list
-   * 3. Using custom model deployments with unique names
-   * 4. Adding experimental or beta models during testing
    *
    * @param provider - The LLM provider (e.g., 'bedrock', 'openai')
    * @param name - The model name/identifier to add
@@ -121,8 +117,7 @@ export class TokenJS implements TokenJSInterface {
    * });
    * ```
    *
-   * Note: When using extended models, you might need to use type casting (`as any`)
-   * for the model parameter until the type definitions are updated to include your custom model.
+   * Note: When using extended models, type casting (`as any`) is required
    */
   extendModelList<
     P extends Exclude<LLMProvider, 'openrouter' | 'openai-compatible'>
@@ -131,6 +126,15 @@ export class TokenJS implements TokenJSInterface {
     if (this.extendedModelExist(provider, name)) {
       return this
     }
+    // If a model name is pre-defined, there is a conflict so we throw an error
+    if (
+      Array.isArray(models[provider].models) &&
+      models[provider].models.includes(name)
+    ) {
+      throw new InputError(
+        `You tried to add the following custom model name: "${name}", for provider: "${provider}". But it conflicts with an existing pre-defined model name. Please try again using different name e.g.: "${name}-custom"`
+      )
+    }
 
     const modelsRef = models[provider] as any
     modelsRef['models'] = [...(models as any)[provider]['models'], name]