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repl: Assignment of _ allowed with warning #5535

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wants to merge 6 commits into from
Closed

repl: Assignment of _ allowed with warning #5535

wants to merge 6 commits into from

Commits on Mar 15, 2016

  1. repl: Assignment of _ allowed with warning 

    This commit addresses #5431 by
changing the way that the repl handles assignment to the global _
variable.

Prior to this commit, node sets the result of the last expression
evaluated in the repl to `_`. This causes problems for users of
underscore, lodash and other packages where it is common to assign
`_` to the package, e.g. `_ = require('lodash');`.

Changes in this commit now result in the following behavior.

- If unassigned on the repl, `_` continues to refer to the last
  evaluated expression.
- If assigned, the default behavior of assigning `_` to the last
  evaluated expression is disabled, and `_` now references whatever
  value was explicitly set. A warning is issued on the repl -
  'expression assignment to _ now disabled'.
- If `_` is assigned multiple times, the warning is only displayed once.
- When `.clear` is executed in the repl, `_` continues to refer to its
  most recent value, whatever that is (this is per existing behavior).
  If `_` had been explicitly set prior to `.clear` it will not change
  again with the evaluation of the next expression.
    @lance
    lance committed Mar 15, 2016
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  2. repl: Reset underscore assignment on .clear 

    Ensures that, when invoking `.clear` in a repl, the underscore
assignment behavior is reset, so that its value is again set to the most
recently evaluated expression.

Additional tests have been added for the behavior of `let` when underscore
assignment has been disabled.
    @lance
    lance committed Mar 15, 2016
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  3. doc: Document _ behavior in REPL. 

    Adds a line of text about the behavior of `_` in the REPL.
    @lance
    lance committed Mar 15, 2016
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  4. repl: Adjust docs for _ usage, and tighten test. 

    Incorporating comments from @cjhrig.
#5535 (comment)
#5535 (comment)
    @lance
    lance committed Mar 15, 2016
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  5. repl: Test _ behavior in REPL_MODE_MAGIC mode. 

    Add a test based on feedback from @cjihrig. Ensures that when used
in 'magic' mode, the behavior of `_` assignment is consistent with
other modes and user expectations.
    @lance
    lance committed Mar 15, 2016
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  6. repl: Change warning text to a complete sentence. 

    When a REPL user explicitly assigns `_` the warning text now reads,
"Expression assignment to _ now disabled.".

Also removed an unnecessary parameter from a test helper function.
    @lance
    lance committed Mar 15, 2016
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