String immutability and template literals

Model answer. Immutable means a string value can never be changed in place. Every "change" creates a new string:

let word = 'cat';
word[0] = 'b';            // silently ignored (TypeError in strict mode)
word = 'b' + word.slice(1);   // 'bat': a new string assigned to the variable

Methods like toUpperCase, replace and trim all return new strings; they never modify the original.

Template literals use backticks and add:

• Interpolation: ` Total: ${qty * price} ` evaluates any expression.
• Multi-line strings without \n.
• Tagged templates: a function processes the parts, used by libraries for safe SQL, CSS-in-JS or translations.

Single and double quotes behave identically; pick one style. Use backticks whenever you insert values, rather than chaining +.