repl: don't color output when TERM=dumb

Fixes: nodejs#26187

lib/repl.js

@@ -501,14 +501,17 @@ function REPLServer(prompt,
   self.writer = options.writer || exports.writer;
 
   if (options.useColors === undefined) {
-    options.useColors = self.terminal;
+    options.useColors = self.terminal && process.env.TERM !== 'dumb';
   }
   self.useColors = !!options.useColors;
 
   if (self.useColors && self.writer === writer) {
     // Turn on ANSI coloring.
     self.writer = (obj) => util.inspect(obj, self.writer.options);
-    self.writer.options = { ...writer.options, colors: true };
+    self.writer.options = {
+      ...writer.options,
+      colors: self.useColors
+    };
   }
 
   function filterInternalStackFrames(structuredStack) {

test/pseudo-tty/repl-dumb-tty.js

@@ -0,0 +1,15 @@
+'use strict';
+require('../common');
+
+process.env.TERM = 'dumb';
+
+const repl = require('repl');
+
+repl.start('> ');
+process.stdin.push('console.log("foo")\n');
+process.stdin.push('1 + 2\n');
+process.stdin.push('"str"\n');
+process.stdin.push('console.dir({ a: 1 })\n');
+process.stdin.push('{ a: 1 }\n');
+process.stdin.push('\n');
+process.stdin.push('.exit\n');

test/pseudo-tty/repl-dumb-tty.out

@@ -0,0 +1,14 @@
+> console.log("foo")
+foo
+undefined
+> 1 + 2
+3
+> "str"
+'str'
+> console.dir({ a: 1 })
+{ a: 1 }
+undefined
+> { a: 1 }
+{ a: 1 }
+>
+> .exit