_.differenceWith(array, [values], [comparator]) source npm package. This method is like _.difference except that it accepts comparator which is invoked to compare elements of array to values.The order and references of result values are determined by the first array.
lodash lets me check for membership of basic data types with includes:
But the following doesn't work:
This confuses me because the following methods that search through a collection seem to do just fine:
What am I doing wrong? How do I check for the membership of an object in a collection with includes ?
edit: question was originally for for lodash version 2.4.1, updated for lodash 4.0.0
2 Answers
The includes (formerly called contains and include) method compares objects by reference (or more precisely, with ). Because the two object literals of {'b': 2} in your example represent different instances, they are not equal. Notice:
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However, this will work because there is only one instance of {'b': 2}:
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On the other hand, the where(deprecated in v4) and find methods compare objects by their properties, so they don't require reference equality. As an alternative to includes, you might want to try some (also aliased as any):
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p.s.w.gp.s.w.gSupplementing the answer by p.s.w.g, here are three other ways of achieving this using lodash4.17.5, without using_.includes():
Say you want to add object entry to an array of objects numbers, only if entry does not exist already.
Download Lodash.assign
If you want to return a Boolean, in the first case, you can check the index that is being returned: