Text, Unicode, and explicit normalization

The idea

A string is immutable: trimming or replacing text produces another string. Decide which changes a task permits before building a pipeline. Trimming ends, collapsing internal spaces, and changing case are different policies. Retain the original when an application needs a faithful display value alongside a normalized search key.

JavaScript string length and numeric indexes count UTF-16 code units. String iteration combines surrogate pairs into code points, so spreading a string can produce fewer elements than its length. Neither measure always counts user-perceived characters, because combining marks and joined emoji can contain several code points. State the unit explicitly; use the simple ASCII subset when an exercise requires byte-like character reasoning.

const original = "  A😀  ";
const text = original.trim();
console.log(text.length, [...text].length);
console.log(original.startsWith("  "));

3 2
true

The emoji occupies two UTF-16 units but one code point. Trimming returns a separate string.