Update undefined@ZLs0NKM0lrnOy5ATDhlk0.md (#6281)

* Update undefined@ZLs0NKM0lrnOy5ATDhlk0.md

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Co-authored-by: dsh <daniel.s.holdsworth@gmail.com>

src/data/roadmaps/javascript/content/undefined@ZLs0NKM0lrnOy5ATDhlk0.md

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 # undefined
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+undefined is a Primitive data type in Javascript.
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+Whenever a variable is declared but not initialized or assigned a value, then it is stored as undefined. A function returns undefined if a value was not returned. A method or statement also returns undefined if the variable that is being evaluated does not have an assigned value.
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+Visit the following resources to learn more:
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+- [@video@undefined in JS](https://www.youtube.com/watch?v=B7iF6G3EyIk&list=PLlasXeu85E9cQ32gLCvAvr9vNaUccPVNP&index=8)