🔰how array methods deal with "holes" ?

JS ⟩ object ⟩ built-in ⟩ Array ⟩ sparse array ⟩ how array methods deal with "holes" ?

👥 相關

• arr.removeValue()

• arr.removeUndefined()

• Array(n) vs. Array(n).fill()

📗 參考

• Better Programming ⟩ What Are Holes in Arrays?

• JavaScript: The Definitive Guide ⟩

  • 7.1.1 Array Literals

  • 7.3 Sparse Arrays

📘 手冊

• Array.prototype method

loops and array methods treat "holes" in sparse arrays differently.

• for-of：treats "holes" as undefined.

• concat — keeps holes

• copyWithin — holes are copied

• entries, keys, values — treats holes as undefined

• every — ignores holes

• fill — fills holes

• filter： removes holes (its result is always a "dense" array). 👉 arr.filter()

• find — treats holes as elements

• findIndex — treats holes as elements

• flat - removes holes but keeps undefined.

• forEach： ignores holes (closure not invoked). 👉 for-of vs. forEach

• indexOf — ignores holes

• join — converts holes to empty strings

• lastIndexOf — ignores holes

• map： preserves holes (but ignored by mapping function)

• pop — treat holes as elements

• push — preserves holes

• reduce , reduceRight— ignores holes

• reverse — preserves holes

• shift — treat holes as undefined

• slice — preserves holes

• sort — preserves holes

• toString — preserves holes

• unshift — preserves holes

• values — converts holes to undefined