Part 12 — Strings

Strings are immutable UTF-16 sequences.

Common methods#

Template literals & tagged templates#

const name = "Ada";
`Hi ${name}, ${1 + 1} lights`;     // interpolation + expressions
`line1
line2`;                            // real newlines

// tagged template: a function receives the parts
function html(strings, ...values) {
  return strings.reduce((out, s, i) =>
    out + s + (values[i] != null ? escape(values[i]) : ""), "");
}
const safe = html`<p>${userInput}</p>`;  // e.g. auto-escaping

Unicode reality ⚠️ 🎯#

"😀".length;               // 2 — it's a surrogate pair, not 1
[..."😀"].length;          // 1 — spread iterates code points
"a".localeCompare("z");    // locale-aware ordering
"café".normalize("NFC");   // combine accent into one code point

Iterating a string with for...of or spread respects code points; indexing by [i] and .length count UTF-16 units.

Regex quick primer#

const re = /(\d{4})-(\d{2})-(\d{2})/;      // groups
"2025-01-31".match(re);                    // ["2025-01-31","2025","01","31",...]
"a1b2".replace(/\d/g, "#");                // "a#b#"
[..."a1b2".matchAll(/(\w)(\d)/g)];         // iterate all matches with groups
/(?<year>\d{4})/.exec("2025").groups.year; // named groups → "2025"

Flags: g global, i ignore case, m multiline, s dotall, u unicode, y sticky, d indices.

Interview questions (Part 12):

1. Why is "😀".length === 2? How do you count real characters?
2. slice vs substring vs substr?
3. Difference between replace and replaceAll; how to replace all with replace?
4. What are tagged templates good for?