[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"verticals":3,"playground-vue-weekly-provide-inject-mutation-trap":44,"search-suggestions":58},[4,20,32],{"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","Read it. Run it. Prove it.","A post a day on modern web development — most with an editable playground and a quiz that explains every answer. Free, no account needed.","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.","Grammar explained the way good documentation explains an API — one idea at a time, each with a quiz.","amber-400","⌘",[13,15,29],"es",{"courses":18,"paths":18,"articles":17,"exams":18,"flashcards":17,"packages":18,"community":17,"certificates":17,"teams":18,"commerce":18},2,{"id":33,"slug":34,"name":35,"tagline":36,"description":37,"accentFrom":38,"accentTo":39,"icon":40,"defaultLocale":13,"locales":41,"features":42,"position":43},"7b3c16f2-931d-410e-802e-e1fa4edab7de","soft","Soft Skills","The half of the job nobody wrote documentation for.","Weekly, on the parts of working life that decide more than your code does — first weeks, meetings, interviews, promotions, and the people around you. Written from what actually happens, and recorded as a podcast you can listen to on the walk.","emerald-400","teal-300","◉",[13],{"courses":18,"paths":18,"articles":17,"exams":18,"flashcards":18,"packages":18,"community":17,"certificates":18,"teams":18,"commerce":18},3,{"slug":45,"title":46,"summary":47,"html":48,"css":49,"js":50,"config":51,"doc":53},"vue-weekly-provide-inject-mutation-trap","Vue provide\u002Finject mutation trap — playground",null,"\u003Cdiv class=\"pg\">\n  \u003Cdiv class=\"pg-title\">🎮 Who can write to the cart?\u003C\u002Fdiv>\n  \u003Cp class=\"pg-sub\">\n    A real Vue \u003Ccode>reactive()\u003C\u002Fcode> cart is \u003Ccode>provide()\u003C\u002Fcode>d from the top. A\n    \u003Ccode><PromoBanner>\u003C\u002Fcode> three levels deep tries to add a free item by mutating\n    the injected value directly, instead of calling the sanctioned \u003Ccode>addItem()\u003C\u002Fcode>.\n    Switch modes to see what \u003Ccode>readonly()\u003C\u002Fcode> actually changes.\n  \u003C\u002Fp>\n\n  \u003Cdiv id=\"boot\" class=\"banner\">\u003C\u002Fdiv>\n\n  \u003Cdiv id=\"app\" hidden>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">1\u003C\u002Fspan> How is the cart provided?\u003C\u002Fdiv>\n      \u003Cdiv class=\"seg\" role=\"group\" aria-label=\"Provide mode\">\n        \u003Cbutton id=\"mode-unprotected\" aria-pressed=\"true\">Unprotected — provide(cart)\u003C\u002Fbutton>\n        \u003Cbutton id=\"mode-protected\" aria-pressed=\"false\">Protected — provide(readonly(cart))\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n      \u003Cdiv class=\"tree\">\n        \u003Cb><CartProvider>\u003C\u002Fb> \u003Cspan class=\"arrow\">provides cart (+ addItem) →\u003C\u002Fspan>\n        \u003Cb><Layout>\u003C\u002Fb> \u003Cspan class=\"arrow\">→\u003C\u002Fspan>\n        \u003Cb><PromoBanner>\u003C\u002Fb> \u003Cspan class=\"arrow\">injects cart\u003C\u002Fspan>\n      \u003C\u002Fdiv>\n      \u003Cdiv class=\"btn-row\">\n        \u003Cbutton class=\"btn bad\" id=\"btn-sneak\">PromoBanner: sneak in a free item\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn primary\" id=\"btn-addItem\">Cart: add item via addItem()\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn ghost\" id=\"btn-reset\">Reset\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n    \u003C\u002Fdiv>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">2\u003C\u002Fspan> Cart state (real Vue reactive state)\u003C\u002Fdiv>\n      \u003Cdiv class=\"cart-box\" id=\"cart-box\">\n        \u003Cdiv class=\"row\">\u003Cspan>(empty)\u003C\u002Fspan>\u003Cspan>\u003C\u002Fspan>\u003C\u002Fdiv>\n      \u003C\u002Fdiv>\n      \u003Cdiv class=\"status\" id=\"status\" style=\"margin-top:12px\">\n        \u003Cspan class=\"dot info\" id=\"dot\">\u003C\u002Fspan>\u003Cspan id=\"statusText\">Ready — try the sneaky mutation in each mode.\u003C\u002Fspan>\n      \u003C\u002Fdiv>\n      \u003Cp class=\"hint\" id=\"hint\">\n        In \u003Cb>Unprotected\u003C\u002Fb> mode, \u003Ccode>PromoBanner\u003C\u002Fcode>'s direct push just works — nothing\n        tells you it happened. In \u003Cb>Protected\u003C\u002Fb> mode, the same line hits Vue's real\n        \u003Ccode>readonly()\u003C\u002Fcode> proxy and is blocked.\n      \u003C\u002Fp>\n    \u003C\u002Fdiv>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">3\u003C\u002Fspan> What actually happened\u003C\u002Fdiv>\n      \u003Cp class=\"hint\" style=\"margin-top:0\">\n        Captures real \u003Ccode>console.warn\u003C\u002Fcode> output from the Vue runtime when it fires —\n        this isn't hand-written warning text.\n      \u003C\u002Fp>\n      \u003Cdiv class=\"log small-log\" id=\"log\" aria-live=\"polite\">\u003C\u002Fdiv>\n    \u003C\u002Fdiv>\n\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\u002F* Demo-specific only — base.css owns tokens, panels, buttons, status, log. *\u002F\n  .cart-box {\n    padding: 12px 14px; border: 1px solid var(--line); border-radius: var(--radius-sm);\n    background: var(--panel-2); font-family: var(--mono); font-size: 0.86rem;\n  }\n  .cart-box .row { display: flex; justify-content: space-between; gap: 10px; padding: 2px 0; }\n  .cart-box .total { margin-top: 8px; padding-top: 8px; border-top: 1px dashed var(--line); font-weight: 700; }\n  .tree { font-size: 0.82rem; color: var(--muted); margin: 8px 0 14px; line-height: 1.7; }\n  .tree b { color: var(--ink); }\n  .tree .arrow { opacity: 0.5; }\n  .small-log .tag { font-family: var(--mono); font-size: 0.72rem; padding: 1px 6px; border-radius: 999px; margin-right: 6px; }\n  .small-log .tag.ok { background: #3fb95022; color: var(--good); }\n  .small-log .tag.blocked { background: #f8514922; color: var(--bad); }\n  .small-log .tag.sys { background: var(--line-soft); color: var(--muted); }","const $ = (s, r = document) => r.querySelector(s);\n\nlet vue;\ntry {\n  \u002F\u002F Pinned to the exact version this article verifies against. ?dev requests\n  \u002F\u002F the development build, which is what makes Vue's readonly() warning print.\n  vue = await import(\"https:\u002F\u002Fesm.sh\u002Fvue@3.5.44?dev\");\n} catch (err) {\n  $(\"#boot\").className = \"banner show info\";\n  $(\"#boot\").innerHTML =\n    \"\u003Cb>Vue couldn't load from the CDN\u003C\u002Fb> — you're offline, or a network policy blocked esm.sh. \" +\n    \"This demo runs the \u003Cem>real\u003C\u002Fem> \u003Ccode>reactive()\u003C\u002Fcode>\u002F\u003Ccode>readonly()\u003C\u002Fcode> proxies, so \" +\n    \"there's nothing honest to show without them. The article's code samples stand on their own; \" +\n    \"try again with a connection.\";\n  throw err;\n}\n\nconst { reactive, readonly, watchEffect } = vue;\n\n$(\"#boot\").hidden = true;\n$(\"#app\").hidden = false;\n\nconst log = $(\"#log\");\nfunction line(tagClass, tagText, text) {\n  const el = document.createElement(\"div\");\n  el.innerHTML = `\u003Cspan class=\"tag ${tagClass}\">${tagText}\u003C\u002Fspan>${text}`;\n  log.prepend(el);\n  while (log.childElementCount > 40) log.lastElementChild.remove();\n}\n\nfunction setStatus(text, kind = \"info\") {\n  $(\"#statusText\").textContent = text;\n  $(\"#dot\").className = \"dot \" + kind;\n}\n\n\u002F\u002F --- The real \"provider\": one reactive cart, one sanctioned mutator ---\nlet cart = reactive({ items: [], total: 0 });\nfunction addItem(item) {\n  cart.items.push(item);\n  cart.total += item.price;\n}\n\nlet protectedMode = false;\n\n\u002F\u002F Capture whatever Vue itself prints when a write to a readonly value fails.\nfunction withWarnCapture(fn) {\n  const captured = [];\n  const original = console.warn;\n  console.warn = (...args) => { captured.push(args.map(String).join(\" \")); };\n  try {\n    fn();\n  } finally {\n    console.warn = original;\n  }\n  return captured;\n}\n\nfunction render() {\n  const box = $(\"#cart-box\");\n  if (cart.items.length === 0) {\n    box.innerHTML = `\u003Cdiv class=\"row\">\u003Cspan>(empty)\u003C\u002Fspan>\u003Cspan>\u003C\u002Fspan>\u003C\u002Fdiv>`;\n  } else {\n    box.innerHTML = cart.items\n      .map((it) => `\u003Cdiv class=\"row\">\u003Cspan>${it.id}\u003C\u002Fspan>\u003Cspan>$${it.price.toFixed(2)}\u003C\u002Fspan>\u003C\u002Fdiv>`)\n      .join(\"\");\n  }\n  box.innerHTML += `\u003Cdiv class=\"row total\">\u003Cspan>Total\u003C\u002Fspan>\u003Cspan>$${cart.total.toFixed(2)}\u003C\u002Fspan>\u003C\u002Fdiv>`;\n}\n\nwatchEffect(render);\n\n$(\"#mode-unprotected\").addEventListener(\"click\", () => setMode(false));\n$(\"#mode-protected\").addEventListener(\"click\", () => setMode(true));\n\nfunction setMode(protect) {\n  protectedMode = protect;\n  $(\"#mode-unprotected\").setAttribute(\"aria-pressed\", String(!protect));\n  $(\"#mode-protected\").setAttribute(\"aria-pressed\", String(protect));\n  line(\n    \"sys\",\n    \"mode\",\n    protect\n      ? `PromoBanner now injects \u003Ccode>readonly(cart)\u003C\u002Fcode> — reads work, writes don't.`\n      : `PromoBanner now injects \u003Ccode>cart\u003C\u002Fcode> directly — the raw reactive object.`\n  );\n  setStatus(\n    protect ? \"Protected mode — try the sneaky mutation.\" : \"Unprotected mode — try the sneaky mutation.\",\n    \"info\"\n  );\n}\n\n$(\"#btn-sneak\").addEventListener(\"click\", () => {\n  \u002F\u002F What PromoBanner actually receives from `inject(\"cart\")` in each mode.\n  const injectedCart = protectedMode ? readonly(cart) : cart;\n  const before = cart.items.length;\n\n  const warnings = withWarnCapture(() => {\n    injectedCart.items.push({ id: \"free-sticker\", price: 0 });\n  });\n\n  const applied = cart.items.length > before;\n\n  if (applied) {\n    line(\"ok\", \"PromoBanner\", `pushed a free item directly — \u003Cb>it worked\u003C\u002Fb>. cart.total is now $${cart.total.toFixed(2)}.`);\n    setStatus(\"Mutation applied. Nothing in Vue noticed — this is the bug.\", \"bad\");\n  } else {\n    const msg = warnings[0] || \"Vue's readonly() set trap returned without applying the write.\";\n    line(\"blocked\", \"PromoBanner\", `tried to push directly — \u003Cb>blocked\u003C\u002Fb>. Vue said: \u003Ccode>${msg}\u003C\u002Fcode>`);\n    setStatus(\"Mutation blocked by readonly(). Cart is unchanged.\", \"good\");\n  }\n});\n\n$(\"#btn-addItem\").addEventListener(\"click\", () => {\n  addItem({ id: \"mug\", price: 12 });\n  line(\"ok\", \"Cart\", `addItem({ id: \"mug\", price: 12 }) — the sanctioned path, works in both modes.`);\n  setStatus(\"Added through addItem() — always allowed, in either mode.\", \"good\");\n});\n\n$(\"#btn-reset\").addEventListener(\"click\", () => {\n  cart.items.splice(0, cart.items.length);\n  cart.total = 0;\n  log.innerHTML = \"\";\n  setStatus(\"Reset — try the sneaky mutation in each mode.\", \"info\");\n});\n\nrender();",{"height":52,"autorun":17},520,{"slug":45,"title":54,"excerpt":55,"coverUrl":56,"vertical":57},"Vue provide\u002Finject: Why You Should Never Skip readonly()","Vue's guide says wrap provide() state in readonly() — most tutorials skip it. The mutation bug that causes, verified against Vue 3.5, plus a cheat sheet.","\u002Fmedia\u002Fcovers\u002Fvue-weekly-provide-inject-mutation-trap.png",{"slug":6},[59,63,67,71,75,79,83,87,91,95,98,102],{"slug":60,"name":61,"articles":62},"webdev","Webdev",166,{"slug":64,"name":65,"articles":66},"javascript","Javascript",133,{"slug":68,"name":69,"articles":70},"frontend","Frontend",94,{"slug":72,"name":73,"articles":74},"tutorial","Tutorial",66,{"slug":76,"name":77,"articles":78},"css","Css",50,{"slug":80,"name":81,"articles":82},"performance","Performance",28,{"slug":84,"name":85,"articles":86},"typescript","Typescript",24,{"slug":88,"name":89,"articles":90},"react","React",20,{"slug":92,"name":93,"articles":94},"programming","Programming",16,{"slug":96,"name":97,"articles":94},"browser","Browser",{"slug":99,"name":100,"articles":101},"node","Node",14,{"slug":103,"name":104,"articles":105},"html","Html",11]