bug#21568: [PATCH] Add prettify-symbols-alist for js-mode

["Simen Heggestøyl" <simenheg@gmail.com>]

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With the introduction of the fat arrow (=>) function notation in
ECMAScript 6, why not make them prettier by default when
prettify-symbols-mode is turned on?

I propose the following patch, which also adds pretty versions of >=
and <= while we're at it:


 From fa37953359f50748801717d259350d7e352cff60 Mon Sep 17 00:00:00 2001
 From: =?UTF-8?q?Simen=20Heggest=C3=B8yl?= <simenheg@gmail.com>
Date: Wed, 23 Sep 2015 21:49:24 +0200
Subject: [PATCH] Add prettify-symbols-alist for js-mode

* lisp/progmodes/js.el (js--prettify-symbols-alist): New defconst.
(js-mode): Use it.
---
 lisp/progmodes/js.el | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/lisp/progmodes/js.el b/lisp/progmodes/js.el
index 6a800f8..f214015 100644
--- a/lisp/progmodes/js.el
+++ b/lisp/progmodes/js.el
@@ -1724,6 +1724,12 @@ This performs fontification according to 
`js--class-styles'."
            (js-syntax-propertize-regexp end))))))
    (point) end))

+(defconst js--prettify-symbols-alist
+  '(("=>" . ?⇒)
+    (">=" . ?≥)
+    ("<=" . ?≤))
+  "Alist of symbol prettifications for JavaScript.")
+
 ;;; Indentation

 (defconst js--possibly-braceless-keyword-re
@@ -3495,6 +3501,7 @@ If one hasn't been set, or if it's stale, prompt 
for a new one."
   (setq-local open-paren-in-column-0-is-defun-start nil)
   (setq-local font-lock-defaults (list js--font-lock-keywords))
   (setq-local syntax-propertize-function #'js-syntax-propertize)
+  (setq-local prettify-symbols-alist js--prettify-symbols-alist)

   (setq-local parse-sexp-ignore-comments t)
   (setq-local parse-sexp-lookup-properties t)
-- 
2.5.1



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