JS Built-in: String, Number, Boolean, Symbol #98

Implement the primitive wrapper built-ins: String, Number, Boolean, and Symbol.

Scope#

String#

• String() constructor and primitive coercion
• String.fromCharCode(), String.fromCodePoint()
• Instance properties: length
• Prototype methods: charAt, charCodeAt, codePointAt
• concat, slice, substring, substr
• indexOf, lastIndexOf, includes, startsWith, endsWith
• trim, trimStart, trimEnd
• padStart, padEnd
• repeat
• split, replace, replaceAll (string pattern — RegExp patterns in RegExp issue)
• toLowerCase, toUpperCase
• at, match, search (basic string patterns)
• toString, valueOf
• String iteration (for...of over code points)

Number#

• Number() constructor and primitive coercion
• Number.isNaN(), Number.isFinite(), Number.isInteger(), Number.isSafeInteger()
• Number.parseInt(), Number.parseFloat()
• Number.EPSILON, Number.MAX_SAFE_INTEGER, Number.MIN_SAFE_INTEGER, Number.MAX_VALUE, Number.MIN_VALUE, NaN, Infinity
• Prototype: toString(radix), toFixed(digits), toPrecision(precision), toExponential(digits), valueOf()
• Global parseInt(), parseFloat(), isNaN(), isFinite()

Boolean#

• Boolean() constructor and truthiness coercion
• Boolean.prototype.toString(), Boolean.prototype.valueOf()

Symbol#

• Symbol(description) factory (not constructable with new)
• Symbol.for(key) and Symbol.keyFor(sym) (global symbol registry)
• Well-known symbols: Symbol.iterator, Symbol.toPrimitive, Symbol.toStringTag, Symbol.hasInstance
• Symbol.prototype.toString(), Symbol.prototype.description
• Symbols as property keys

Acceptance Criteria#

• String methods produce correct results (test each)
• Number parsing and formatting work correctly
• Boolean coercion follows truthiness rules
• Symbol creation and global registry work
• Well-known symbols are defined
• Primitive auto-boxing works (e.g., "hello".length)
• Unit tests for each method

Phase 10 — JavaScript Engine (issue 9 of 15). Depends on: JS core built-ins (Object/Function/Array/Error).