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Array<T>

Legend:

• ✏️ method changes this.
• 🔒 method does not change this.

Array<T>.prototype.*:

• concat(...items: Array): T[] 🔒 ^ES3

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Strings

String.prototype.*

None of the string methods modify this – they always return fresh strings.

• charAt(pos: number): string ^ES1

  Returns the character at index pos, as a string (JavaScript does not have a datatype for characters). str[i] is equivalent to str.charAt(i) and more concise (caveat: may not work on old engines).