readline: add option to stop duplicates in history

Adds `options.deDupeHistory` for `readline.createInterface(options)`. If
`options.deDupeHistory` is `true`, when a new input line being added to
the history list duplicates an older one, removes the older line from
the list. Defaults to `false`.

Many users would appreciate this option, as it is a common setting in
shells. This option certainly should not be default behavior, as it
would be problematic in applications such as the `repl`, which inherits
from the readline `Interface`.

Extends documentation to reflect this API addition.

Adds tests for when `options.deDupeHistory` is truthy, and when
`options.deDupeHistory` is falsey.

PR-URL: https://github.com/nodejs/node/pull/2982
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/doc/api/readline.md b/doc/api/readline.md
index 878721bb4d..e471daecae 100644
--- a/doc/api/readline.md
+++ b/doc/api/readline.md
@@ -370,6 +370,9 @@ changes:
     `crlfDelay` milliseconds, both `\r` and `\n` will be treated as separate
     end-of-line input. Default to `100` milliseconds.
     `crlfDelay` will be coerced to `[100, 2000]` range.
+  * `deDupeHistory` {boolean} If `true`, when a new input line added to the
+    history list duplicates an older one, this removes the older line from the
+    list. Defaults to `false`.
 
 The `readline.createInterface()` method creates a new `readline.Interface`
 instance.