<pre class="shiki github-dark shaku"><code>class MyURLSearchParams { #searchParams = new Map() #orderedEntries = [] constructor(init) { if (!init?.trim()) return if (init[0] === '?') init = init.slice(1) const params = init.split('&amp;') for (const pair of params) { const [key, ...rest] = pair.split('=') this.append( decodeURIComponent(key.replaceAll('+', ' ')), decodeURIComponent(rest.join('=').replaceAll('+', ' ')) ) } } append(name, value) { value = String(value) if (!this.#searchParams.has(name)) this.#searchParams.set(name, []) this.#searchParams.get(name).push(value) this.#orderedEntries.push([name, value]) } delete(name) { if (!this.#searchParams.delete(name)) return this.#orderedEntries = this.#orderedEntries.filter(([key]) =&gt; key !== name) } *entries() { yield* this.#orderedEntries } *keys() { yield* this.#orderedEntries.map(([key]) =&gt; key) } *values() { yield* this.#orderedEntries.map(([, value]) =&gt; value) } forEach(callback) { for (const [key, value] of this) { callback(value, key) } } get(name) { return this.#searchParams.get(name)?.[0] ?? null } getAll(name) { return [...(this.#searchParams.get(name) ?? [])] } has(name) { return this.#searchParams.has(name) } set(name, value) { value = String(value) if (!this.#searchParams.has(name)) { this.#orderedEntries.push([name, value]) } else { const newEntries = [] let firstEntryReplaced = false for (const [k, v] of this.#orderedEntries) { if (k !== name) { newEntries.push([k, v]) } if (k === name &amp;&amp; !firstEntryReplaced) { newEntries.push([k, value]) firstEntryReplaced = true } } this.#orderedEntries = newEntries } this.#searchParams.set(name, [value]) } sort() { this.#orderedEntries.sort(([a], [b]) =&gt; a.localeCompare(b)) } toString() { return this.#orderedEntries .map(([k, v]) =&gt; `${encodeURIComponent(k)}=${encodeURIComponent(v)}`) .join('&amp;') .replaceAll('%20', '+') } *[Symbol.iterator]() { yield* this.entries() }}</code></pre>

Implementing URLSearchParams: Map for Lookup, Array for Ordering

When we want to extract parameters from query string, URLSearchParams could be very handy. Can you implement MyURLSearchParams which works the same ? …