From 80a0d9334ddb7d77342e33b62198e2c9d71dd5d5 Mon Sep 17 00:00:00 2001
From: Wiktor Owczarek <tikolu43@gmail.com>
Date: Fri, 27 Feb 2026 13:38:21 +0000
Subject: [PATCH] Add suport for custom tag types

---
 src/compile-string.ts |  6 +++++-
 src/config.ts         |  4 ++++
 src/parse.ts          | 21 ++++++++++-----------
 3 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/src/compile-string.ts b/src/compile-string.ts
index aab453b5..64808b72 100644
--- a/src/compile-string.ts
+++ b/src/compile-string.ts
@@ -95,7 +95,7 @@ export function compileBody(this: Eta, buff: Array<AstObject>): string {
       // we know string exists
       returnStr += "__eta.res+='" + str + "';\n";
     } else {
-      const type = currentBlock.t; // "r", "e", or "i"
+      const type = currentBlock.t; // "r", "e", "i" or custom tag name
       let content = currentBlock.val || "";
 
       if (config.debug) returnStr += "__eta.line=" + currentBlock.lineNo + "\n";
@@ -123,6 +123,10 @@ export function compileBody(this: Eta, buff: Array<AstObject>): string {
       } else if (type === "e") {
         // execute
         returnStr += content + "\n";
+
+      } else if (type in config.customTags) {
+        const customTag = config.customTags[type];
+        returnStr += `__eta.res += this.config.customTags['${type}']('${content}', ${config.varName});\n`;
       }
     }
   }
diff --git a/src/config.ts b/src/config.ts
index af436109..f7ba7b61 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -27,6 +27,9 @@ export interface EtaConfig {
   /** Holds cache of resolved filepaths. Set to `false` to disable. */
   cacheFilepaths: boolean;
 
+  /** Object specifying custom tags. Keys are tag prefixes, values are functions which take tag content and return a string. */
+  customTags: Record<string, (content: string, data: unknown) => string>;
+
   /** Whether to pretty-format error messages (introduces runtime penalties) */
   debug: boolean;
 
@@ -89,6 +92,7 @@ const defaultConfig: EtaConfig = {
   autoTrim: [false, "nl"],
   cache: false,
   cacheFilepaths: true,
+  customTags: {},
   debug: false,
   escapeFunction: XMLEscape,
   // default filter function (not used unless enables) just stringifies the input
diff --git a/src/parse.ts b/src/parse.ts
index bb74db77..028ceead 100644
--- a/src/parse.ts
+++ b/src/parse.ts
@@ -2,10 +2,8 @@ import { ParseErr } from "./err.ts";
 import type { Eta } from "./internal.ts";
 import { trimWS } from "./utils.ts";
 
-export type TagType = "r" | "e" | "i" | "";
-
 export interface TemplateObject {
-  t: TagType;
+  t: string;
   val: string;
   lineNo?: number;
 }
@@ -40,6 +38,8 @@ export function parse(this: Eta, str: string): Array<AstObject> {
   let lastIndex = 0;
   const parseOptions = config.parse;
 
+  const customTagPrefixes = Object.keys(config.customTags)
+
   if (config.plugins) {
     for (let i = 0; i < config.plugins.length; i++) {
       const plugin = config.plugins[i];
@@ -90,6 +90,7 @@ export function parse(this: Eta, str: string): Array<AstObject> {
     parseOptions.exec,
     parseOptions.interpolate,
     parseOptions.raw,
+    ...customTagPrefixes,
   ].reduce((accumulator, prefix) => {
     if (accumulator && prefix) {
       return accumulator + "|" + escapeRegExp(prefix);
@@ -138,14 +139,12 @@ export function parse(this: Eta, str: string): Array<AstObject> {
 
         trimLeftOfNextStr = closeTag[2];
 
-        const currentType: TagType =
-          prefix === parseOptions.exec
-            ? "e"
-            : prefix === parseOptions.raw
-              ? "r"
-              : prefix === parseOptions.interpolate
-                ? "i"
-                : "";
+        let currentType = "";
+        if(prefix === config.parse.exec) currentType = "e";
+        else if(prefix === config.parse.interpolate) currentType = "i";
+        else if(prefix === config.parse.raw) currentType = "r";
+        // custom tags
+        else if(customTagPrefixes.includes(prefix)) currentType = prefix;
 
         currentObj = { t: currentType, val: content };
         break;