Enable flattening to a specified depth (continued) #2868
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Per a new TC39 proposal http://bterlson.github.io/proposal-flatMap/#sec-Array.prototype.flatten they're suggesting a depth argument. This was fairly trivial to implement without breaking the current functionality. Thoughts?
This is mostly to ensure that the internal flatten is still well-behaved, since it being called internally with boolean arguments, and there is no check in place to enforce that false is interpreted as infinite depth.
Manual testing revealed that flattening with depth=false behaved as a shallow flatten instead of a deep one.
jashkenas
approved these changes
Jul 28, 2020
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Thanks for the review @jashkenas! |
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This is a continuation of #2460 by @paulfalgout. The former boolean
shallowparameter of both the internal and the externalflattenis replaced by adepthparameter which can be either boolean or numeric. Boolean values still have the same meaning. Numeric1has the same meaning astruewhile0or less results in a shallow copy without any flattening. The default is still infinite depth.@jashkenas The original PR was approved by @akre54 and @michaelficarra in 2016. If this is sufficiently reassuring for you, you can stop reading here.
@paulfalgout I moved your checks against nonnumeric and nonpositive
depthvalues back from the public to the internalflatten. At the time, you were concerned that this would be inconsistent withstrict === true, but there is actually no conflict. Whendepth === 1, every nested element of every array is copied whether the nested element is an array or not, even whenstrict === true. Extrapolating this todepth === 0, "every array" is just the top-level array, so every element of it should be copied, regardless of whether it is an array and regardless of the value ofstrict.Merging this should automatically also merge #2460.