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terrierscript
terrierscript

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Process `string | string[]` item with `flat()` and `map()`

#typescript #todayilearned #javascript

In some case, we meet string|string[] type (I meet this on next.js)

I found this can process simply with flat() and map() (Not flatMap())

function appendC(strOrArr : string | string[]) : string[] { return [strOrArr].flat().map( item => item + "c" ) } appendC("a") // ["ac"] appendC(["aa", "bb") // ["aac", "bbc"]

If you need generate array in map, you can use flatMap

function splitItems(strOrArr : string | string[]): string[]{ return [strOrArr].flat().flatMap( item => item.split(",") ) } splitItems("a,b") // ["ac"] splitItems(["aa,bb", "bb,cc") // ["aac", "bbc"]

In addition, if you need process deep array (like [1,[1,2,[1,2,3],2],[3,2]]), you can use flat(Infinity)

[deepArray].flat(Infinity).map(...

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