20 files changed, 750 insertions, 0 deletions

diff --git a/typescript/src/AjaxResponse.ts b/typescript/src/AjaxResponse.ts
new file mode 100644
index 0000000..8b578a8
--- /dev/null
+++ b/typescript/src/AjaxResponse.ts
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+import type Pod from "./Pod.js";
+
+export default AjaxResponse;
+
+type AjaxResponse = Readonly<{
+  queryresult?: {
+    pods?: Pod[];
+  };
+}>;
diff --git a/typescript/src/AjaxSettings.ts b/typescript/src/AjaxSettings.ts
new file mode 100644
index 0000000..b5b4cf4
--- /dev/null
+++ b/typescript/src/AjaxSettings.ts
@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+import AppID from "./AppID.js";
+import EntrypointParameter from "./EntrypointParameter.js";
+
+export default AjaxSettings;
+
+type AjaxSettings = Readonly<{
+  url: "https://api.wolframalpha.com/v2/query";
+  dataType: "jsonp";
+  traditional: true;
+  data: Readonly<
+    EntrypointParameter & {
+      appid: AppID;
+      output: "json";
+      reinterpret: true;
+      podtimeout: 30;
+      scantimeout: 30;
+      parsetimeout: 30;
+      totaltimeout: 30;
+      formattimeout: 30;
+    }
+  >;
+}>;
+
+// Wolfram|Alpha Full Results API Reference
+// https://products.wolframalpha.com/api/documentation
+
+// jQuery.ajax() | jQuery API Documentation
+// https://api.jquery.com/jQuery.ajax/
diff --git a/typescript/src/AppID.ts b/typescript/src/AppID.ts
new file mode 100644
index 0000000..af4edb2
--- /dev/null
+++ b/typescript/src/AppID.ts
@@ -0,0 +1,5 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+export default AppID;
+
+type AppID = "H9V325-HTALUWHKGK" | "AKJTJT-LR5LL8WTG6" | "LKY83U-XW6ATU9URU";
diff --git a/typescript/src/EntrypointParameter.ts b/typescript/src/EntrypointParameter.ts
new file mode 100644
index 0000000..f78f1fc
--- /dev/null
+++ b/typescript/src/EntrypointParameter.ts
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+export default EntrypointParameter;
+
+type EntrypointParameter = Readonly<{
+  input: string;
+  i2d?: true;
+  podstate: Readonly<
+    ["Step-by-step solution", "Step-by-step", "Show all steps", string?]
+  >;
+}>;
diff --git a/typescript/src/Pod.ts b/typescript/src/Pod.ts
new file mode 100644
index 0000000..169ff5a
--- /dev/null
+++ b/typescript/src/Pod.ts
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+import type State from "./State.js";
+import type SubPod from "./SubPod.js";
+
+export default Pod;
+
+type Pod = Readonly<{
+  title?: string;
+  states?: State[];
+  subpods?: SubPod[];
+}>;
diff --git a/typescript/src/State.ts b/typescript/src/State.ts
new file mode 100644
index 0000000..e3bb35e
--- /dev/null
+++ b/typescript/src/State.ts
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+export default State;
+
+type State = Readonly<{
+  value?: string;
+  states?: {
+    name?: string;
+  }[];
+}>;
diff --git a/typescript/src/SubPod.ts b/typescript/src/SubPod.ts
new file mode 100644
index 0000000..1e26a87
--- /dev/null
+++ b/typescript/src/SubPod.ts
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+export default SubPod;
+
+type SubPod = Readonly<{
+  img?: {
+    src?: string;
+    alt?: string;
+  };
+  plaintext?: string;
+}>;
diff --git a/typescript/src/entrypoint.ts b/typescript/src/entrypoint.ts
new file mode 100644
index 0000000..e939d92
--- /dev/null
+++ b/typescript/src/entrypoint.ts
@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+import type EntrypointParameter from "./EntrypointParameter.js";
+import getAjaxResponse from "./getAjaxResponse.js";
+import getAjaxSettings from "./getAjaxSettings.js";
+import getNewHTML from "./getNewHTML.js";
+import listenToChangeEvent from "./listenToChangeEvent.js";
+import placeholder from "./placeholder.js";
+import reRenderComponent from "./reRenderComponent.js";
+import setContentEditable from "./setContentEditable.js";
+import typescriptExhaustive from "./typescriptExhaustive.js";
+
+export default async (
+  EntrypointParameter: EntrypointParameter
+): Promise<void> => {
+  try {
+    Object.freeze(EntrypointParameter);
+    typescriptExhaustive(EntrypointParameter);
+
+    window.scroll(0, 0);
+    reRenderComponent(placeholder);
+
+    const AjaxSettings = getAjaxSettings(EntrypointParameter);
+    const AjaxResponse = await getAjaxResponse(AjaxSettings);
+    const newHTML = getNewHTML(AjaxSettings, AjaxResponse);
+    reRenderComponent(newHTML);
+
+    listenToChangeEvent(EntrypointParameter);
+    setContentEditable();
+  } catch (error) {
+    console.warn({ error });
+  }
+};
diff --git a/typescript/src/getAjaxResponse.ts b/typescript/src/getAjaxResponse.ts
new file mode 100644
index 0000000..1459114
--- /dev/null
+++ b/typescript/src/getAjaxResponse.ts
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+import AjaxResponse from "./AjaxResponse.js";
+import type AjaxSettings from "./AjaxSettings.js";
+
+export default async (AjaxSettings: AjaxSettings): Promise<AjaxResponse> => {
+  try {
+    Object.freeze(AjaxSettings);
+
+    // npm i @types/jquery
+    return Object.freeze(await jQuery.ajax(AjaxSettings));
+  } catch (error) {
+    console.warn({ error });
+    return {};
+  }
+};
diff --git a/typescript/src/getAjaxSettings.ts b/typescript/src/getAjaxSettings.ts
new file mode 100644
index 0000000..5899637
--- /dev/null
+++ b/typescript/src/getAjaxSettings.ts
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+import AjaxSettings from "./AjaxSettings.js";
+import EntrypointParameter from "./EntrypointParameter.js";
+import getAppID from "./getAppID.js";
+
+export default (EntrypointParameter: EntrypointParameter): AjaxSettings =>
+  Object.freeze({
+    url: "https://api.wolframalpha.com/v2/query",
+    dataType: "jsonp",
+    traditional: true,
+    data: Object.freeze({
+      ...EntrypointParameter,
+      appid: getAppID(),
+      output: "json",
+      reinterpret: true,
+      podtimeout: 30,
+      scantimeout: 30,
+      parsetimeout: 30,
+      totaltimeout: 30,
+      formattimeout: 30,
+    }),
+  });
diff --git a/typescript/src/getAppID.ts b/typescript/src/getAppID.ts
new file mode 100644
index 0000000..eed7e1b
--- /dev/null
+++ b/typescript/src/getAppID.ts
@@ -0,0 +1,67 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+import AppID from "./AppID.js";
+import typescriptNever from "./typescriptNever.js";
+
+/**
+ * To generate a new AppID, please follow these steps:
+ *
+ *  1. Open Tor Browser and go to:
+ *     https://products.wolframalpha.com/api/
+ *  2. Click the orange "Get API Access" button.
+ *     Tor Browser will redirect you to:
+ *     https://account.wolfram.com/login/oauth2/sign-in
+ *  3. Click the red "Create one" hyperlink to create a new Wolfram ID.
+ *     Tor Browser will redirect you to:
+ *     https://account.wolfram.com/login/create
+ *  4. Fill out the form with random alphanumeric characters.
+ *  5. Click the red "Create Wolfram ID" button.
+ *     Tor Browser will redirect you to:
+ *     https://developer.wolframalpha.com/portal/myapps/index.html
+ *  6. Click the orange "Sign up to get your first AppID" button.
+ *  7. Fill out the form with random alphanumeric characters.
+ *  8. Click the orange "Sign up" button.
+ *  9. Click the orange "Get an AppID" button.
+ * 10. Fill out the form with random alphanumeric characters.
+ * 11. Click the orange "Get AppID" button.
+ */
+const appIDArray: Readonly<AppID[]> = Object.freeze([
+  "H9V325-HTALUWHKGK",
+  "AKJTJT-LR5LL8WTG6",
+  "LKY83U-XW6ATU9URU",
+]);
+
+console.assert(appIDArray.length > 0);
+
+appIDArray.forEach((appID) => {
+  console.assert(appID.length === 17);
+  console.assert(/[0-9A-Z]{6}-[0-9A-Z]{10}/.test(appID));
+});
+
+export default (): AppID => {
+  const random = appIDArray[getRandomInt() % appIDArray.length];
+
+  if (typeof random === "string") {
+    return random;
+  } else if (random === undefined) {
+    console.warn({ random });
+  } else {
+    typescriptNever(random);
+  }
+
+  return "H9V325-HTALUWHKGK";
+};
+
+const getRandomInt = (): number => {
+  const random = crypto.getRandomValues(new Uint32Array(1))[0];
+
+  if (typeof random === "number") {
+    return random;
+  } else if (random === undefined) {
+    console.warn({ random });
+  } else {
+    typescriptNever(random);
+  }
+
+  return 0;
+};
diff --git a/typescript/src/getNewHTML.ts b/typescript/src/getNewHTML.ts
new file mode 100644
index 0000000..f5d2070
--- /dev/null
+++ b/typescript/src/getNewHTML.ts
@@ -0,0 +1,199 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+import type AjaxResponse from "./AjaxResponse.js";
+import type AjaxSettings from "./AjaxSettings.js";
+import type Pod from "./Pod.js";
+import PodsClassName from "./podsClassName.js";
+import type State from "./State.js";
+import type SubPod from "./SubPod.js";
+
+export default (
+  AjaxSettings: AjaxSettings,
+  AjaxResponse: AjaxResponse
+): string =>
+  `
+    <div class="${PodsClassName}">
+      <div>
+        <div>
+          <section>
+            ${
+              // Wolfram Alpha does have some limitations when it comes to processing certain types of input.
+              // When "input" is an empty string,
+              // the "pods" property will not be present in the "queryresult" object.
+              // To see an example of an empty input string,
+              // visit the following URL:
+              // https://www.wolframalpha.com/input?i=
+              Object.freeze(AjaxResponse) === undefined
+                ? (console.warn({ AjaxResponse }), "")
+                : AjaxResponse.queryresult === undefined
+                ? (console.warn({ AjaxResponse }), "")
+                : AjaxResponse.queryresult.pods === undefined
+                ? "" // console.warn
+                : AjaxResponse.queryresult.pods.map(buildPod).join("")
+            }
+            <section>
+              <div>
+                <h2>
+                  Technical information
+                </h2>
+              </div>
+              <div> </div>
+              <div>
+                <div>
+                  <div>
+                    <details>
+                      <div>
+                        If you have programming knowledge, feel free to explore the technical information provided below:
+                      </div>
+                      <textarea name="technical-information">${
+                        Object.freeze(AjaxSettings) === undefined
+                          ? (console.warn({ AjaxSettings }), "")
+                          : Object.freeze(AjaxResponse) === undefined
+                          ? (console.warn({ AjaxResponse }), "")
+                          : escapeHTML(tryStringify(AjaxSettings, AjaxResponse))
+                      }</textarea>
+                    </details>
+                  </div>
+                </div>
+              </div>
+              <div> </div>
+            </section>
+          </section>
+        </div>
+      </div>
+    </div>
+  `;
+
+const buildPod = (pod: Pod): string =>
+  `
+    <section>
+      <div>
+        ${
+          pod.title === undefined
+            ? (console.warn({ pod }), "")
+            : `<h2>${escapeHTML(pod.title)}</h2>`
+        }
+        ${
+          // In most cases, pods are stateless and do not have specific states.
+          // As a result, the "states" property of "pod" is typically undefined.
+          pod.states === undefined
+            ? "" // console.warn
+            : pod.states.map(buildSelectElement).join("")
+        }
+      </div>
+      <div> </div>
+      ${
+        pod.subpods === undefined
+          ? (console.warn({ pod }), "")
+          : pod.subpods.map(buildSubpod).join("")
+      }
+    </section>
+  `;
+
+const buildSelectElement = (state: State): string =>
+  // Although it is possible to handle the scenario where the "states" property is undefined,
+  // implementing the necessary logic may result in a cluttered user interface.
+  // This challenge is primarily due to my limited expertise in front-end design.
+  // Consequently, the current implementation of the parsing logic is still insufficient in addressing the situation where the "states" property is undefined.
+  state.states === undefined
+    ? "" // console.warn
+    : `
+        <select name="pod-states">
+          ${
+            state.value === undefined
+              ? (console.warn({ state }), "")
+              : `
+                  <option>${escapeHTML(state.value)}</option>
+                `
+          }
+          ${state.states.map(buildOption).join("")}
+        </select>
+      `;
+
+const buildOption = (state: { name?: string }): string =>
+  state.name === undefined
+    ? (console.warn({ state }), "")
+    : `
+        <option>${escapeHTML(state.name)}</option>
+      `;
+
+const buildSubpod = (subpod: SubPod): string =>
+  `
+    ${
+      subpod.img === undefined
+        ? (console.warn({ subpod }), "")
+        : `
+            <div>
+              <div>
+                <img
+                  src="${escapeHTML(
+                    subpod.img.src === undefined
+                      ? (console.warn({ subpod }), "")
+                      : subpod.img.src
+                  )}"
+                  alt="${escapeHTML(
+                    subpod.img.alt === undefined
+                      ? (console.warn({ subpod }), "")
+                      : subpod.img.alt
+                  )}"
+                >
+              </div>
+            </div>
+          `
+    }
+    ${
+      subpod.plaintext === undefined
+        ? (console.warn({ subpod }), "")
+        : `
+            <div style="font-family: monospace; overflow: auto;">
+              <div>
+                <div>
+                  <details>
+                    <summary style="direction: rtl;"></summary>
+                    <div>
+                      <pre>${escapeHTML(subpod.plaintext)}</pre>
+                    </div>
+                    <br />
+                  </details>
+                </div>
+              </div>
+            </div>
+          `
+    }
+  `;
+
+const tryStringify = (
+  AjaxSettings: AjaxSettings,
+  AjaxResponse: AjaxResponse
+): string => {
+  try {
+    return JSON.stringify(
+      {
+        document,
+        AjaxSettings,
+        AjaxResponse,
+      },
+      null,
+      4
+    );
+  } catch (error) {
+    console.warn({ error });
+    return error instanceof TypeError ? error.message + "\n" + error.stack : "";
+    // JSON.stringify() - JavaScript | MDN
+    // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify#exceptions
+  }
+};
+
+const escapeHTML = (unsafeHTML: string): string =>
+  unsafeHTML
+    .replace(/&/g, "&amp;")
+    .replace(/</g, "&lt;")
+    .replace(/>/g, "&gt;")
+    .replace(/"/g, "&quot;")
+    .replace(/'/g, "&#039;");
+
+// Can I escape HTML special chars in JavaScript? - Stack Overflow
+// https://stackoverflow.com/questions/6234773/can-i-escape-html-special-chars-in-javascript
+
+// test case:
+// https://www.wolframalpha.com/input?i=solve+%7By%27%28x%29+%3D+-2+y%2C+y%280%29%3D1%7D+from+0+to+10+using+r+k+f+algorithm
diff --git a/typescript/src/listenToChangeEvent.ts b/typescript/src/listenToChangeEvent.ts
new file mode 100644
index 0000000..7f091a9
--- /dev/null
+++ b/typescript/src/listenToChangeEvent.ts
@@ -0,0 +1,52 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+import type EntrypointParameter from "./EntrypointParameter.js";
+import entrypoint from "./entrypoint.js";
+import podsClassName from "./podsClassName.js";
+import typescriptNever from "./typescriptNever.js";
+
+export default (EntrypointParameter: EntrypointParameter): void => {
+  try {
+    Object.freeze(EntrypointParameter);
+
+    Array.from(
+      document.querySelectorAll(
+        `html > body > div#__next > div > main > main > div.${podsClassName} > div > div > section > section > div:is(:first-child) > select`
+      )
+    )
+      .filter((element: Element): boolean => {
+        if (element instanceof HTMLSelectElement) {
+          return true;
+        } else if (element instanceof Element) {
+          console.warn({ element });
+        } else {
+          typescriptNever(element);
+        }
+
+        return false;
+      })
+      .map((element: Element): void => {
+        element.addEventListener("change", async (event): Promise<void> => {
+          if (event.target instanceof HTMLSelectElement) {
+            await entrypoint({
+              ...EntrypointParameter,
+              podstate: [
+                "Step-by-step solution",
+                "Step-by-step",
+                "Show all steps",
+                event.target.value,
+              ],
+            });
+          } else if (event.target instanceof EventTarget) {
+            console.warn({ event });
+          } else if (event.target === null) {
+            console.warn({ event });
+          } else {
+            typescriptNever(event.target);
+          }
+        });
+      });
+  } catch (error) {
+    console.warn({ error });
+  }
+};
diff --git a/typescript/src/onload.ts b/typescript/src/onload.ts
new file mode 100644
index 0000000..6c864ad
--- /dev/null
+++ b/typescript/src/onload.ts
@@ -0,0 +1,94 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+import typescriptNever from "./typescriptNever.js";
+
+export default addEventListener(
+  "load",
+  (): void => (
+    setTimeout(
+      (): void =>
+        console.assert(
+          Array.from(
+            document.querySelectorAll(
+              // To select the form element, we use different selectors depending on the input mode.
+              // If the input mode is "natural language", the form is a direct child of the section element, so we use the selector "section > form".
+              // However, if the input mode is "math input", the form is a direct child of the div element, so we use the selector "div > form".
+              `
+                html > body > #__next > div > main > main > div > div > section > form > div > div > input,
+                html > body > #__next > div > main > main > div > div > div       form > div > div > input
+              `
+            )
+          )
+            .filter((element: Element): boolean => {
+              if (element instanceof HTMLInputElement) {
+                return true;
+              } else if (element instanceof Element) {
+                console.warn({ element });
+              } else {
+                typescriptNever(element);
+              }
+
+              return false;
+            })
+            .map((element: Element): void => {
+              if (element instanceof HTMLElement) {
+                element.focus();
+              } else if (element instanceof Element) {
+                console.warn({ element });
+              } else {
+                typescriptNever(element);
+              }
+            }).length === 1
+        ),
+      1000
+    ),
+    [
+      (): void =>
+        Array.from(
+          document.querySelectorAll(
+            // The positioning of the ul element is dynamically adjusted to ensure it adapts well to different viewport widths.
+            // To specifically target the ul element when the viewport width is larger, we use the selector "div:is(:first-child) > ul".
+            // Conversely, to target the ul element when the viewport width is smaller, we use the selector "div:is(:first-child) + ul".
+            `
+              html > body > #__next > div > main > main > div > div > div > section > section > div:is(:first-child) > ul > li,
+              html > body > #__next > div > main > main > div > div > div > section > section > div:is(:first-child) + ul > li
+            `
+          )
+        )
+          .filter((element: Element): boolean => {
+            if (element instanceof HTMLLIElement) {
+              return true;
+            } else if (element instanceof Element) {
+              console.warn({ element });
+            } else {
+              typescriptNever(element);
+            }
+
+            return false;
+          })
+          .forEach((element: Element): void => {
+            if (element instanceof HTMLElement) {
+              if (element.innerHTML.includes("Step-by-step")) {
+                element.style.display = "none";
+              } else {
+              }
+            } else if (element instanceof Element) {
+              console.warn({ element });
+            } else {
+              typescriptNever(element);
+            }
+          }),
+      (): void => {
+        document.title = document.title.replace(
+          "- Wolfram|Alpha",
+          "- Free Wolfram|Alpha Step-by-step Solution - Wolfree"
+        );
+      },
+    ].map(
+      (callback: () => void): void => (
+        setInterval(callback, 2000), addEventListener("click", callback)
+      )
+    ),
+    scroll(0, 0)
+  )
+);
diff --git a/typescript/src/placeholder.ts b/typescript/src/placeholder.ts
new file mode 100644
index 0000000..083226c
--- /dev/null
+++ b/typescript/src/placeholder.ts
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+export default `
+  <div class="wolfree-pods wolfree-placeholder">
+    <div>
+      <div>
+        <div><div></div></div>
+        <div><div></div></div>
+        <div><div></div></div>
+      </div>
+    </div>
+  </div>
+`;
diff --git a/typescript/src/podsClassName.ts b/typescript/src/podsClassName.ts
new file mode 100644
index 0000000..fea9f4c
--- /dev/null
+++ b/typescript/src/podsClassName.ts
@@ -0,0 +1,3 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+export default "wolfree-pods";
diff --git a/typescript/src/reRenderComponent.ts b/typescript/src/reRenderComponent.ts
new file mode 100644
index 0000000..f73fd1a
--- /dev/null
+++ b/typescript/src/reRenderComponent.ts
@@ -0,0 +1,70 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+import podsClassName from "./podsClassName.js";
+import typescriptNever from "./typescriptNever.js";
+
+export default (newHTML: string): void => {
+  try {
+    console.assert(
+      Array.from(
+        document.querySelectorAll(
+          `html > body > #__next > div > main > main > div.${podsClassName}`
+        )
+      )
+        .filter((element: Element): boolean => {
+          if (element instanceof HTMLDivElement) {
+            return true;
+          } else if (element instanceof Element) {
+            console.warn({ element });
+          } else {
+            typescriptNever(element);
+          }
+
+          return false;
+        })
+        .map((element: Element): void => {
+          if (element instanceof Element) {
+            element.remove();
+          } else {
+            typescriptNever(element);
+          }
+        }).length <= 1
+    );
+
+    console.assert(
+      Array.from(
+        document.querySelectorAll(
+          "html > body > #__next > div > main > main > div:nth-of-type(1)"
+        )
+      )
+        .filter((element: Element): boolean => {
+          if (element instanceof HTMLDivElement) {
+            return true;
+          } else if (element instanceof Element) {
+            console.warn({ element });
+          } else if (element === null) {
+            console.warn({ element });
+          } else {
+            typescriptNever(element);
+          }
+
+          return false;
+        })
+        .map((element: Element): void => {
+          if (element instanceof Element) {
+            element.insertAdjacentHTML(
+              "afterend",
+              // npm i @types/dompurify
+              globalThis.DOMPurify.sanitize(newHTML)
+            );
+          } else if (element === null) {
+            console.warn({ element });
+          } else {
+            typescriptNever(element);
+          }
+        }).length === 1
+    );
+  } catch (error) {
+    console.warn({ error });
+  }
+};
diff --git a/typescript/src/setContentEditable.ts b/typescript/src/setContentEditable.ts
new file mode 100644
index 0000000..ebfe423
--- /dev/null
+++ b/typescript/src/setContentEditable.ts
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+import podsClassName from "./podsClassName.js";
+import typescriptNever from "./typescriptNever.js";
+
+export default (): void => {
+  try {
+    Array.from(
+      document.querySelectorAll(
+        `html > body > div#__next > div > main > main > div.${podsClassName} > div > div > section > section > div > div > div > details > div`
+      )
+    )
+      .filter((element: Element): boolean => {
+        if (element instanceof HTMLDivElement) {
+          return true;
+        } else if (element instanceof Element) {
+          console.warn({ element });
+        } else {
+          typescriptNever(element);
+        }
+
+        return false;
+      })
+      .map((element: Element): void => {
+        if (element instanceof Element) {
+          element.setAttribute("contenteditable", "");
+        } else {
+          typescriptNever(element);
+        }
+      });
+  } catch (error) {
+    console.warn({ error });
+  }
+};
diff --git a/typescript/src/typescriptExhaustive.ts b/typescript/src/typescriptExhaustive.ts
new file mode 100644
index 0000000..656a419
--- /dev/null
+++ b/typescript/src/typescriptExhaustive.ts
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+import type EntrypointParameter from "./EntrypointParameter.js";
+import typescriptNever from "./typescriptNever.js";
+
+export default (EntrypointParameter: EntrypointParameter): void => {
+  Object.freeze(EntrypointParameter);
+
+  if (typeof EntrypointParameter.input !== "string") {
+    typescriptNever(EntrypointParameter.input);
+  }
+
+  if (EntrypointParameter.i2d !== true) {
+    if (EntrypointParameter.i2d !== undefined) {
+      typescriptNever(EntrypointParameter.i2d);
+    }
+  }
+
+  if (!(EntrypointParameter.podstate instanceof Array)) {
+    typescriptNever(EntrypointParameter.podstate);
+  }
+
+  if (EntrypointParameter.podstate.length !== 3) {
+    if (EntrypointParameter.podstate.length !== 4) {
+      typescriptNever(EntrypointParameter.podstate.length);
+    }
+  }
+
+  if (EntrypointParameter.podstate[0] !== "Step-by-step solution") {
+    typescriptNever(EntrypointParameter.podstate[0]);
+  }
+
+  if (EntrypointParameter.podstate[1] !== "Step-by-step") {
+    typescriptNever(EntrypointParameter.podstate[1]);
+  }
+
+  if (EntrypointParameter.podstate[2] !== "Show all steps") {
+    typescriptNever(EntrypointParameter.podstate[2]);
+  }
+
+  if (typeof EntrypointParameter.podstate[3] !== "string") {
+    if (typeof EntrypointParameter.podstate[3] !== "undefined") {
+      typescriptNever(EntrypointParameter.podstate[3]);
+    }
+  }
+};
diff --git a/typescript/src/typescriptNever.ts b/typescript/src/typescriptNever.ts
new file mode 100644
index 0000000..42becd5
--- /dev/null
+++ b/typescript/src/typescriptNever.ts
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+
+export default (typescriptNeverValue: never): never => {
+  console.warn({ typescriptNeverValue });
+
+  return typescriptNeverValue;
+};
+
+// How do I check that a switch block is exhaustive in TypeScript? - Stack Overflow
+// https://stackoverflow.com/questions/39419170/how-do-i-check-that-a-switch-block-is-exhaustive-in-typescript