[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"verticals":3,"playground-weekly-cors-explained":32},[4,20],{"id":5,"slug":6,"name":7,"tagline":8,"description":9,"accentFrom":10,"accentTo":11,"icon":12,"defaultLocale":13,"locales":14,"features":16,"position":19},"019fe637-3d33-714b-b57f-23e163ffca0c","dev","Web Development","Build. Learn. Ship.","Practical courses, engineering-grade articles and open-source tools for people who ship.","violet-500","cyan-400","◇","en",[13,15],"fa",{"courses":17,"paths":17,"articles":17,"exams":18,"flashcards":18,"packages":17,"community":17,"certificates":17,"teams":17,"commerce":17},true,false,0,{"id":21,"slug":22,"name":23,"tagline":24,"description":25,"accentFrom":26,"accentTo":10,"icon":27,"defaultLocale":13,"locales":28,"features":30,"position":31},"019fe637-3dc2-754c-8657-0f175bfee7c6","lang","Languages","Learn a language the way you learn a codebase.","Structured paths, listening drills and spaced repetition that actually sticks.","amber-400","⌘",[13,15,29],"es",{"courses":17,"paths":17,"articles":18,"exams":18,"flashcards":18,"packages":18,"community":17,"certificates":18,"teams":18,"commerce":17},2,{"slug":33,"title":34,"summary":35,"html":36,"css":37,"js":38,"config":39,"doc":41},"weekly-cors-explained","CORS request simulator — interactive playground",null,"\u003Cdiv class=\"pg\">\n    \u003Ch1 class=\"pg-title\">🎮 CORS request simulator\u003C\u002Fh1>\n    \u003Cp class=\"pg-sub\">\n      You're \u003Ccode>https:\u002F\u002Fapp.example.com\u003C\u002Fcode>, calling an API on a different origin.\n      Pick a request shape, a credentials setting, and the server's CORS config — then send it\n      and watch exactly what the browser does step by step.\n    \u003C\u002Fp>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">1\u003C\u002Fspan> Request shape\u003C\u002Fdiv>\n      \u003Cdiv class=\"seg\" id=\"bodySeg\" role=\"group\" aria-label=\"Content type\">\n        \u003Cbutton data-val=\"simple\" aria-pressed=\"true\">text\u002Fplain (simple)\u003C\u002Fbutton>\n        \u003Cbutton data-val=\"json\" aria-pressed=\"false\">application\u002Fjson (preflighted)\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n      \u003Cp class=\"hint\">A safelisted content type is sent directly. \u003Ccode>application\u002Fjson\u003C\u002Fcode> is not\n        on the safelist, so the browser asks permission first with an \u003Ccode>OPTIONS\u003C\u002Fcode> preflight.\u003C\u002Fp>\n\n      \u003Clabel class=\"toggle\" style=\"margin-top:10px\">\n        \u003Cinput type=\"checkbox\" id=\"creds\" \u002F>\u003Cspan class=\"switch\">\u003C\u002Fspan>\n        \u003Cspan>Send cookies (\u003Ccode>credentials: \"include\"\u003C\u002Fcode>)\u003C\u002Fspan>\n      \u003C\u002Flabel>\n      \u003Cp class=\"hint\">Requires the server to allow credentials explicitly — and to name your\n        exact origin, never a wildcard.\u003C\u002Fp>\n    \u003C\u002Fdiv>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">2\u003C\u002Fspan> Server's CORS configuration\u003C\u002Fdiv>\n      \u003Cdiv class=\"seg\" id=\"serverSeg\" role=\"group\" aria-label=\"Server CORS header\">\n        \u003Cbutton data-val=\"none\" aria-pressed=\"true\">No CORS header\u003C\u002Fbutton>\n        \u003Cbutton data-val=\"star\" aria-pressed=\"false\">\u003Ccode>*\u003C\u002Fcode>\u003C\u002Fbutton>\n        \u003Cbutton data-val=\"match\" aria-pressed=\"false\">Exact match\u003C\u002Fbutton>\n        \u003Cbutton data-val=\"mismatch\" aria-pressed=\"false\">Wrong origin\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n      \u003Cdiv class=\"presets\" style=\"margin-top:14px\">\n        \u003Cbutton class=\"btn sm\" data-preset=\"works\">Worked example: it works\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn sm\" data-preset=\"wildcard-creds\">Worked example: the wildcard trap\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n    \u003C\u002Fdiv>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">3\u003C\u002Fspan> Send it\u003C\u002Fdiv>\n      \u003Cdiv class=\"btn-row\">\n        \u003Cbutton class=\"btn primary\" id=\"send\">Send request\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn ghost\" id=\"reset\">Reset\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n\n      \u003Cdiv class=\"flow\" id=\"flow\" style=\"margin-top:14px\">\n        \u003Cspan class=\"box\" id=\"f-origin\">app.example.com\u003C\u002Fspan>\n        \u003Cspan class=\"arrow\">→\u003C\u002Fspan>\n        \u003Cspan class=\"box\" id=\"f-preflight\">preflight?\u003C\u002Fspan>\n        \u003Cspan class=\"arrow\">→\u003C\u002Fspan>\n        \u003Cspan class=\"box\" id=\"f-server\">server\u003C\u002Fspan>\n        \u003Cspan class=\"arrow\">→\u003C\u002Fspan>\n        \u003Cspan class=\"box\" id=\"f-js\">your JS\u003C\u002Fspan>\n      \u003C\u002Fdiv>\n\n      \u003Cdiv class=\"status\" id=\"status\" style=\"margin-top:14px\">\n        \u003Cspan class=\"dot info\" id=\"dot\">\u003C\u002Fspan>\u003Cspan id=\"statusText\">Ready — pick a config and send.\u003C\u002Fspan>\n      \u003C\u002Fdiv>\n\n      \u003Cdiv class=\"step-log\" id=\"log\" style=\"margin-top:8px\">\u003C\u002Fdiv>\n    \u003C\u002Fdiv>\n  \u003C\u002Fdiv>","\u002F*\n * Shared playground design system — daily-post\n * ============================================\n * Link it from any post's playground\u002Findex.html (no per-post boilerplate):\n *\n *   \u003Clink rel=\"stylesheet\" href=\"..\u002F..\u002F..\u002Fplayground\u002Fassets\u002Fbase.css\" \u002F>\n *\n * The relative path resolves the same locally (posts\u002F\u003Cbase>\u002Fplayground\u002F) and on\n * the deployed host (public\u002Fposts\u002F\u003Cbase>\u002Fplayground\u002F), because build-site.js\n * mirrors this file to public\u002Fplayground\u002Fassets\u002Fbase.css. For a CodeSandbox\n * --embed, playground.js inlines this file so the single-file sandbox still styles.\n *\n * Then write ONLY the demo-specific CSS in your inline \u003Cstyle>. Everything below\n * — tokens, layout, panels, buttons, toggles, sliders, code blocks, status\u002Flog,\n * banners, presets — comes for free and looks consistent across every post.\n *\n * Theme-aware: dark by default, light via prefers-color-scheme AND a\n * [data-theme] override on \u003Chtml> (so a toggle can force either). Accessible:\n * real focus rings, adequate contrast, reduced-motion honored.\n *\u002F\n\n\u002F* ---------- design tokens ---------- *\u002F\n:root {\n  --bg: #0d1117;\n  --bg-grid: #ffffff0a;\n  --panel: #161b22;\n  --panel-2: #0b0e14;\n  --card: #0b0e14;\n  --ink: #e8ebf2;\n  --muted: #9aa4b2;\n  --faint: #6b7688;\n  --line: #232a35;\n  --line-soft: #ffffff12;\n  --accent: #7c9cff;\n  --accent-ink: #0b0e14;\n  --good: #3fb950;\n  --warn: #f0883e;\n  --bad: #f85149;\n  --info: #58a6ff;\n  --radius: 14px;\n  --radius-sm: 9px;\n  --shadow: 0 8px 30px #0006;\n  --shadow-sm: 0 4px 14px #0005;\n  --mono: ui-monospace, SFMono-Regular, \"SF Mono\", Menlo, Consolas, \"Liberation Mono\", monospace;\n  --sans: ui-sans-serif, system-ui, -apple-system, \"Segoe UI\", Roboto, \"Helvetica Neue\", sans-serif;\n  color-scheme: dark;\n}\n\n\u002F* Light theme — system preference, overridable by [data-theme] on \u003Chtml>. *\u002F\n@media (prefers-color-scheme: light) {\n  :root:not([data-theme=\"dark\"]) {\n    --bg: #f4f6fb;\n    --bg-grid: #00000008;\n    --panel: #ffffff;\n    --panel-2: #f0f3f9;\n    --card: #f7f9fc;\n    --ink: #131722;\n    --muted: #5b6472;\n    --faint: #8a93a3;\n    --line: #e2e7f0;\n    --line-soft: #00000010;\n    --accent: #2f6df0;\n    --accent-ink: #ffffff;\n    --good: #1a7f37;\n    --warn: #bc4c00;\n    --bad: #cf222e;\n    --info: #0969da;\n    --shadow: 0 8px 30px #0000001f;\n    --shadow-sm: 0 4px 14px #00000014;\n    color-scheme: light;\n  }\n}\n:root[data-theme=\"light\"] {\n  --bg: #f4f6fb;\n  --bg-grid: #00000008;\n  --panel: #ffffff;\n  --panel-2: #f0f3f9;\n  --card: #f7f9fc;\n  --ink: #131722;\n  --muted: #5b6472;\n  --faint: #8a93a3;\n  --line: #e2e7f0;\n  --line-soft: #00000010;\n  --accent: #2f6df0;\n  --accent-ink: #ffffff;\n  --good: #1a7f37;\n  --warn: #bc4c00;\n  --bad: #cf222e;\n  --info: #0969da;\n  --shadow: 0 8px 30px #0000001f;\n  --shadow-sm: 0 4px 14px #00000014;\n  color-scheme: light;\n}\n\n\u002F* ---------- reset & base ---------- *\u002F\n*, *::before, *::after { box-sizing: border-box; }\n\nbody {\n  margin: 0;\n  min-height: 100vh;\n  font-family: var(--sans);\n  color: var(--ink);\n  background:\n    radial-gradient(circle at 1px 1px, var(--bg-grid) 1px, transparent 0) 0 0 \u002F 24px 24px,\n    var(--bg);\n  display: flex;\n  justify-content: center;\n  align-items: flex-start;\n  padding: clamp(14px, 3vw, 26px);\n  line-height: 1.55;\n  -webkit-font-smoothing: antialiased;\n  text-rendering: optimizeLegibility;\n}\n\n\u002F* The single content column. *\u002F\n.pg {\n  width: 100%;\n  max-width: 860px;\n}\n\n\u002F* ---------- header ---------- *\u002F\n.pg-title {\n  font-size: clamp(1.15rem, 1rem + 1vw, 1.4rem);\n  font-weight: 800;\n  letter-spacing: -0.02em;\n  margin: 0 0 4px;\n  display: flex;\n  align-items: center;\n  gap: 9px;\n}\n.pg-sub {\n  color: var(--muted);\n  font-size: 0.92rem;\n  line-height: 1.5;\n  margin: 0 0 16px;\n  max-width: 66ch;\n}\n.pg-sub strong, .pg-sub b { color: var(--ink); font-weight: 700; }\n.pg-sub code { font-family: var(--mono); background: var(--line-soft); color: var(--accent);\n  padding: 1px 6px; border-radius: 6px; font-size: 0.85em; }\n\n\u002F* ---------- panels ---------- *\u002F\n.panel {\n  background: var(--panel);\n  border: 1px solid var(--line);\n  border-radius: var(--radius);\n  padding: 16px 18px;\n  margin-bottom: 14px;\n  box-shadow: var(--shadow-sm);\n}\n.panel-label {\n  font-size: 0.7rem;\n  text-transform: uppercase;\n  letter-spacing: 0.08em;\n  color: var(--muted);\n  font-weight: 800;\n  margin: 0 0 13px;\n  display: flex;\n  align-items: center;\n  gap: 8px;\n}\n.panel-label .n {\n  display: inline-grid; place-items: center;\n  width: 18px; height: 18px; border-radius: 50%;\n  background: var(--accent); color: var(--accent-ink);\n  font-size: 0.66rem; font-weight: 800;\n}\n\n\u002F* ---------- layout helpers ---------- *\u002F\n.row { display: flex; flex-wrap: wrap; gap: 12px; align-items: center; }\n.row.between { justify-content: space-between; }\n.col { display: flex; flex-direction: column; gap: 10px; }\n.grow { flex: 1 1 0; min-width: 0; }\n.wrap-controls { display: flex; flex-wrap: wrap; gap: 16px 24px; align-items: flex-end; }\n.field { display: flex; flex-direction: column; gap: 7px; min-width: 0; }\n.field > .label, .ctl-label {\n  font-size: 0.7rem; text-transform: uppercase; letter-spacing: 0.04em;\n  color: var(--muted); font-weight: 800;\n}\n\n\u002F* ---------- buttons ---------- *\u002F\n.btn {\n  font: inherit; font-weight: 650; font-size: 0.88rem;\n  cursor: pointer; user-select: none;\n  border: 1px solid var(--line);\n  background: var(--card); color: var(--ink);\n  padding: 9px 15px; border-radius: var(--radius-sm);\n  display: inline-flex; align-items: center; gap: 8px;\n  transition: background .15s ease, border-color .15s ease, transform .05s ease, color .15s ease;\n}\n.btn:hover { background: var(--line-soft); border-color: var(--muted); }\n.btn:active { transform: translateY(1px); }\n.btn:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }\n.btn[disabled] { opacity: 0.45; cursor: not-allowed; }\n.btn.primary { background: var(--accent); border-color: var(--accent); color: var(--accent-ink); }\n.btn.primary:hover { filter: brightness(1.08); background: var(--accent); }\n.btn.good { background: var(--good); border-color: var(--good); color: #04140a; }\n.btn.bad  { background: var(--bad);  border-color: var(--bad);  color: #fff; }\n.btn.ghost { background: transparent; }\n.btn.sm { padding: 6px 11px; font-size: 0.82rem; }\n\n.btn-row { display: flex; flex-wrap: wrap; gap: 9px; }\n\n\u002F* Segmented control — a row of buttons where one is active (aria-pressed). *\u002F\n.seg { display: inline-flex; background: var(--card); border: 1px solid var(--line);\n  border-radius: var(--radius-sm); padding: 3px; gap: 3px; }\n.seg button {\n  font: inherit; font-weight: 650; font-size: 0.84rem; cursor: pointer;\n  border: none; background: transparent; color: var(--muted);\n  padding: 7px 13px; border-radius: 7px;\n  transition: background .15s ease, color .15s ease;\n}\n.seg button:hover { color: var(--ink); }\n.seg button[aria-pressed=\"true\"] { background: var(--accent); color: var(--accent-ink); }\n.seg button:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }\n\n\u002F* Preset chips — worked-example shortcuts. *\u002F\n.presets { display: flex; flex-wrap: wrap; gap: 8px; }\n.presets .btn { background: var(--panel-2); }\n\n\u002F* ---------- toggle switch ---------- *\u002F\n.toggle { display: inline-flex; align-items: center; gap: 10px; cursor: pointer;\n  font-size: 0.88rem; font-weight: 600; user-select: none; }\n.toggle input { position: absolute; opacity: 0; width: 0; height: 0; }\n.switch { position: relative; width: 44px; height: 25px; border-radius: 999px; flex: none;\n  background: var(--line); border: 1px solid var(--line); transition: background .18s ease; }\n.switch::after { content: \"\"; position: absolute; top: 2px; left: 2px; width: 19px; height: 19px;\n  border-radius: 50%; background: #cfd6e4; transition: transform .18s ease; box-shadow: 0 1px 3px #0006; }\n.toggle input:checked + .switch { background: var(--good); border-color: var(--good); }\n.toggle input:checked + .switch::after { transform: translateX(19px); background: #fff; }\n.toggle input:focus-visible + .switch { outline: 2px solid var(--accent); outline-offset: 2px; }\n\n\u002F* ---------- range slider ---------- *\u002F\ninput[type=\"range\"] {\n  -webkit-appearance: none; appearance: none; width: 100%; height: 6px;\n  background: var(--line); border-radius: 999px; outline: none; cursor: pointer; margin: 8px 0;\n}\ninput[type=\"range\"]::-webkit-slider-thumb {\n  -webkit-appearance: none; appearance: none; width: 19px; height: 19px; border-radius: 50%;\n  background: var(--accent); border: 2px solid var(--panel); box-shadow: var(--shadow-sm); cursor: pointer;\n}\ninput[type=\"range\"]::-moz-range-thumb {\n  width: 19px; height: 19px; border-radius: 50%; background: var(--accent);\n  border: 2px solid var(--panel); box-shadow: var(--shadow-sm); cursor: pointer;\n}\ninput[type=\"range\"]:focus-visible { outline: 2px solid var(--accent); outline-offset: 3px; }\n\n\u002F* ---------- text inputs \u002F selects ---------- *\u002F\ninput[type=\"text\"], input[type=\"number\"], input[type=\"search\"], select, textarea {\n  font: inherit; color: var(--ink); background: var(--card);\n  border: 1px solid var(--line); border-radius: var(--radius-sm); padding: 8px 11px; width: 100%;\n}\ntextarea { font-family: var(--mono); font-size: 0.85rem; line-height: 1.6; resize: vertical; }\ninput:focus-visible, select:focus-visible, textarea:focus-visible {\n  outline: 2px solid var(--accent); outline-offset: 1px; border-color: var(--accent);\n}\n\n\u002F* ---------- status \u002F output \u002F log ---------- *\u002F\n.status {\n  display: flex; align-items: center; gap: 9px; flex-wrap: wrap;\n  font-size: 0.9rem; font-weight: 600;\n  padding: 11px 14px; border-radius: var(--radius-sm);\n  background: var(--panel-2); border: 1px solid var(--line); color: var(--ink);\n}\n.status.good { border-color: color-mix(in srgb, var(--good) 55%, var(--line)); }\n.status.warn { border-color: color-mix(in srgb, var(--warn) 55%, var(--line)); }\n.status.bad  { border-color: color-mix(in srgb, var(--bad) 55%, var(--line)); }\n.dot { width: 9px; height: 9px; border-radius: 50%; background: var(--muted); flex: none; }\n.dot.good { background: var(--good); } .dot.warn { background: var(--warn); }\n.dot.bad { background: var(--bad); } .dot.info { background: var(--info); }\n\n.output { background: var(--panel-2); border: 1px solid var(--line); border-radius: var(--radius-sm);\n  padding: 13px 15px; }\n.log { font-family: var(--mono); font-size: 0.8rem; line-height: 1.7; background: var(--card);\n  border: 1px solid var(--line); border-radius: var(--radius-sm); padding: 11px 14px;\n  max-height: 220px; overflow-y: auto; white-space: pre-wrap; }\n\n\u002F* ---------- code block + syntax tokens ---------- *\u002F\n.code {\n  font-family: var(--mono); font-size: 0.82rem; line-height: 1.7;\n  background: var(--panel-2); border: 1px solid var(--line); border-radius: var(--radius-sm);\n  padding: 13px 15px; overflow-x: auto; white-space: pre; tab-size: 2;\n}\n.code .tok-sel  { color: var(--accent); }\n.code .tok-prop { color: #86e29b; }\n.code .tok-kw   { color: #ff9bcb; }\n.code .tok-str  { color: #f0c674; }\n.code .tok-num  { color: #f0883e; }\n.code .tok-cmt  { color: var(--faint); font-style: italic; }\n.code .hl { background: color-mix(in srgb, var(--good) 22%, transparent); border-radius: 4px; padding: 0 3px; }\n\n\u002F* ---------- hint \u002F caption ---------- *\u002F\n.hint { font-size: 0.83rem; color: var(--muted); line-height: 1.55; margin: 10px 0 0; }\n.hint code { font-family: var(--mono); color: var(--ink); background: var(--line-soft);\n  padding: 1px 5px; border-radius: 5px; font-size: 0.86em; }\n.hint strong { color: var(--ink); }\n\n\u002F* ---------- banner (feature-support \u002F notices) ---------- *\u002F\n.banner {\n  display: none; margin-bottom: 14px; padding: 11px 14px; border-radius: 11px;\n  font-size: 0.85rem; line-height: 1.5;\n  color: var(--ink); background: color-mix(in srgb, var(--warn) 12%, var(--panel));\n  border: 1px solid color-mix(in srgb, var(--warn) 45%, var(--line));\n}\n.banner.show { display: block; }\n.banner.info { background: color-mix(in srgb, var(--info) 12%, var(--panel));\n  border-color: color-mix(in srgb, var(--info) 45%, var(--line)); }\n.banner code { font-family: var(--mono); background: var(--line-soft); padding: 1px 5px; border-radius: 5px; }\n\n\u002F* ---------- misc atoms ---------- *\u002F\n.pill { display: inline-flex; align-items: center; gap: 6px; font-size: 0.75rem; font-weight: 700;\n  padding: 3px 9px; border-radius: 999px; background: var(--line-soft); color: var(--muted); }\n.pill.good { color: var(--good); background: color-mix(in srgb, var(--good) 16%, transparent); }\n.pill.bad  { color: var(--bad);  background: color-mix(in srgb, var(--bad) 16%, transparent); }\n.mono { font-family: var(--mono); }\n.muted { color: var(--muted); }\n.big-num { font-family: var(--mono); font-size: 1.6rem; font-weight: 800; letter-spacing: -0.02em; }\n\n\u002F* Optional theme toggle button (top-right). Wire it in JS if you want it. *\u002F\n.theme-btn { position: fixed; top: 12px; right: 12px; z-index: 20; }\n\n\u002F* ---------- responsive ---------- *\u002F\n@media (max-width: 560px) {\n  .panel { padding: 14px; }\n  .wrap-controls { gap: 14px; }\n  .btn { padding: 9px 13px; }\n}\n\n\u002F* ---------- reduced motion ---------- *\u002F\n@media (prefers-reduced-motion: reduce) {\n  *, *::before, *::after { transition-duration: 0.01ms !important; animation-duration: 0.01ms !important; }\n}\n\n\n.flow { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; font-size: 0.9rem; }\n  .flow .box {\n    padding: 6px 10px; border: 1px solid var(--line); border-radius: var(--radius-sm);\n    background: var(--panel-2); white-space: nowrap;\n  }\n  .flow .arrow { color: var(--muted); font-size: 1rem; }\n  .flow .box.active { border-color: var(--accent); color: var(--accent); }\n  .step-log .step { padding: 6px 0; border-bottom: 1px dashed var(--line); }\n  .step-log .step:last-child { border-bottom: none; }\n  .step-log .tag {\n    display: inline-block; font-size: 0.72rem; font-weight: 600; letter-spacing: 0.02em;\n    padding: 1px 6px; border-radius: 999px; margin-right: 6px; text-transform: uppercase;\n  }\n  .tag.browser { background: color-mix(in srgb, var(--accent) 22%, transparent); color: var(--accent); }\n  .tag.server { background: color-mix(in srgb, #22c55e 22%, transparent); color: #22c55e; }\n  .tag.result { background: color-mix(in srgb, #ef4444 22%, transparent); color: #ef4444; }","\"use strict\";\n  const $ = (id) => document.getElementById(id);\n  const state = { body: \"simple\", creds: false, server: \"none\" };\n\n  function wireSeg(id, onPick) {\n    const el = $(id);\n    el.querySelectorAll(\"button\").forEach((btn) => {\n      btn.addEventListener(\"click\", () => {\n        el.querySelectorAll(\"button\").forEach((b) => b.setAttribute(\"aria-pressed\", \"false\"));\n        btn.setAttribute(\"aria-pressed\", \"true\");\n        onPick(btn.dataset.val);\n      });\n    });\n  }\n  wireSeg(\"bodySeg\", (v) => (state.body = v));\n  wireSeg(\"serverSeg\", (v) => (state.server = v));\n  $(\"creds\").addEventListener(\"change\", (e) => (state.creds = e.target.checked));\n\n  function setStatus(text, kind) {\n    $(\"statusText\").textContent = text;\n    $(\"dot\").className = \"dot \" + kind;\n  }\n\n  function resetFlow() {\n    [\"f-origin\", \"f-preflight\", \"f-server\", \"f-js\"].forEach((id) => $(id).classList.remove(\"active\"));\n  }\n\n  function addStep(tag, text) {\n    const row = document.createElement(\"div\");\n    row.className = \"step\";\n    row.innerHTML = '\u003Cspan class=\"tag ' + tag + '\">' + tag + \"\u003C\u002Fspan>\" + text;\n    $(\"log\").appendChild(row);\n  }\n\n  function run() {\n    $(\"log\").innerHTML = \"\";\n    resetFlow();\n    const needsPreflight = state.body === \"json\";\n\n    $(\"f-origin\").classList.add(\"active\");\n    addStep(\"browser\", \"Page on \u003Ccode>https:\u002F\u002Fapp.example.com\u003C\u002Fcode> calls \u003Ccode>fetch()\u003C\u002Fcode>.\");\n\n    if (needsPreflight) {\n      $(\"f-preflight\").classList.add(\"active\");\n      $(\"f-preflight\").textContent = \"OPTIONS sent\";\n      addStep(\n        \"browser\",\n        \"Body is \u003Ccode>application\u002Fjson\u003C\u002Fcode> — not CORS-safelisted, so the browser sends an \" +\n          \"\u003Ccode>OPTIONS\u003C\u002Fcode> preflight before the real request.\"\n      );\n      addStep(\"server\", \"Server answers the preflight with its configured CORS headers.\");\n    } else {\n      $(\"f-preflight\").textContent = \"skipped\";\n      addStep(\"browser\", \"Body is \u003Ccode>text\u002Fplain\u003C\u002Fcode> — a simple request. No preflight; sent directly.\");\n    }\n\n    $(\"f-server\").classList.add(\"active\");\n    let allowOriginHeader = \"(none)\";\n    if (state.server === \"star\") allowOriginHeader = \"*\";\n    if (state.server === \"match\") allowOriginHeader = \"https:\u002F\u002Fapp.example.com\";\n    if (state.server === \"mismatch\") allowOriginHeader = \"https:\u002F\u002Fother-app.example.com\";\n    addStep(\"server\", \"Response includes \u003Ccode>Access-Control-Allow-Origin: \" + allowOriginHeader + \"\u003C\u002Fcode>.\");\n\n    \u002F\u002F Evaluate the outcome.\n    let allowed = false;\n    let reason = \"\";\n\n    if (state.creds && state.server === \"star\") {\n      allowed = false;\n      reason = \"A wildcard (\u003Ccode>*\u003C\u002Fcode>) cannot be combined with credentials. Browsers reject this pairing outright, even though the header is present.\";\n    } else if (state.server === \"none\") {\n      allowed = false;\n      reason = \"No \u003Ccode>Access-Control-Allow-Origin\u003C\u002Fcode> header at all — the browser has nothing to check against, so it blocks the response.\";\n    } else if (state.server === \"mismatch\") {\n      allowed = false;\n      reason = \"The header names a different origin than the page making the request — it doesn't match, so the response is blocked.\";\n    } else {\n      allowed = true;\n      reason = state.server === \"star\"\n        ? \"Wildcard with no credentials is a valid, if broad, allow-all — the response is readable.\"\n        : \"The header matches this page's exact origin — the response is readable by your JavaScript.\";\n    }\n\n    if (allowed) {\n      $(\"f-js\").classList.add(\"active\");\n      addStep(\"result\", \"✅ \" + reason);\n      setStatus(\"Success — your JS receives the response body.\", \"good\");\n    } else {\n      addStep(\"result\", \"❌ \" + reason);\n      setStatus(\"Blocked — fetch() rejects; the server may have still run.\", \"bad\");\n    }\n  }\n\n  $(\"send\").addEventListener(\"click\", run);\n  $(\"reset\").addEventListener(\"click\", () => {\n    $(\"log\").innerHTML = \"\";\n    resetFlow();\n    setStatus(\"Ready — pick a config and send.\", \"info\");\n  });\n\n  function applyPreset(name) {\n    if (name === \"works\") {\n      state.body = \"json\"; state.creds = false; state.server = \"match\";\n      $(\"bodySeg\").querySelectorAll(\"button\").forEach((b) => b.setAttribute(\"aria-pressed\", b.dataset.val === \"json\" ? \"true\" : \"false\"));\n      $(\"serverSeg\").querySelectorAll(\"button\").forEach((b) => b.setAttribute(\"aria-pressed\", b.dataset.val === \"match\" ? \"true\" : \"false\"));\n      $(\"creds\").checked = false;\n    } else if (name === \"wildcard-creds\") {\n      state.body = \"json\"; state.creds = true; state.server = \"star\";\n      $(\"bodySeg\").querySelectorAll(\"button\").forEach((b) => b.setAttribute(\"aria-pressed\", b.dataset.val === \"json\" ? \"true\" : \"false\"));\n      $(\"serverSeg\").querySelectorAll(\"button\").forEach((b) => b.setAttribute(\"aria-pressed\", b.dataset.val === \"star\" ? \"true\" : \"false\"));\n      $(\"creds\").checked = true;\n    }\n    run();\n  }\n  document.querySelectorAll(\"[data-preset]\").forEach((btn) => {\n    btn.addEventListener(\"click\", () => applyPreset(btn.dataset.preset));\n  });",{"height":40,"autorun":17},520,{"slug":33,"title":42,"excerpt":43,"coverUrl":44},"CORS Explained: The Complete Guide (with Cheat Sheet)","A complete guide to CORS: the same-origin policy, preflight requests, and Access-Control-Allow-Origin headers — with worked examples and a cheat sheet.","\u002Fmedia\u002Fcovers\u002Fweekly-cors-explained.png"]