Render initial undefined values #377
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expected '<div></div>' to equal '<div attribute="it\'s undefined"></div>'
For initial renders, _equalToPreviousValues must always return false. The other checks will return true if all values in the part are undefined, meaning attributes can get lost. See lit#375
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Awesome fix, thanks! |
neuronetio
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Dec 2, 2019
Make `AttributePart#_equalToPreviousValues` always return false in the initial render For initial renders, _equalToPreviousValues must always return false. The other checks will return true if all values in the part are undefined, meaning attributes can get lost. See lit#375
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As mentioned in #375, if all values for an AttributePart or PropertyPart are
undefined, the initial render will not set the attribute/property. See this comment for an explanation as to why that's wrong.Instead of adding an extra property to check for the initial render and introducing logic to update the property on the first render I simply added a check on the length of
this._previousValue, as that array can only be empty for the initial render (the property is set to an empty array in the constructor;setValuealways sets the property to a non-empty array).