diff --git a/scripts/ts-smoosh/README.md b/scripts/ts-smoosh/README.md
new file mode 100644
index 0000000000..e1c25b1d85
--- /dev/null
+++ b/scripts/ts-smoosh/README.md
@@ -0,0 +1,32 @@
+## TS Smoosh
+
+Combine type decls with related source files.
+
+
+# Use
+
+Given a JavaScript file (or list of files) like so:
+
+```
+$ node ts-smoosh/bin ./src/some-file.js
+```
+
+Will produce `.jsx` files using nearby `.d.ts` files.
+
+
+# Running Tests
+
+```
+$ node test
+```
+
+Test cases live in various directories in `./tests`. Tests run by comparing the output against golden master `.tsx` files. To update the masters, run `node ts-smoosh/bin ./test/0X-dir/somefile.js`.
+
+# Notes
+
+Here are articles and docs I that were helpful when writing this script.
+
+- [Using the Compiler API](https://github.com/microsoft/TypeScript/wiki/Using-the-Compiler-API)
+- [Blog post about using TS's parser directly](https://medium.com/allenhwkim/how-to-parse-typescript-from-source-643387971f4e)
+- [TypeScript compiler APIs revisited](https://blog.scottlogic.com/2017/05/02/typescript-compiler-api-revisited.html)
+- [TypeScript API Playground on Glitch](https://typescript-api-playground.glitch.me/#example=Transformation%203)
diff --git a/scripts/ts-smoosh/bin.js b/scripts/ts-smoosh/bin.js
new file mode 100644
index 0000000000..680d97252c
--- /dev/null
+++ b/scripts/ts-smoosh/bin.js
@@ -0,0 +1,13 @@
+const { smoosh } = require("./smoosh");
+
+// Given an array of `.js` files, smooshes their .d.ts declarations and
+// produces a .tsx file.
+
+const without = (ending) => (fileName) =>
+  fileName.endsWith(ending)
+    ? fileName.substr(0, fileName.length - ending.length)
+    : fileName;
+
+const files = process.argv.slice(2);
+
+files.map(without(".js")).map(smoosh);
diff --git a/scripts/ts-smoosh/smoosh.js b/scripts/ts-smoosh/smoosh.js
new file mode 100644
index 0000000000..a06d7507dc
--- /dev/null
+++ b/scripts/ts-smoosh/smoosh.js
@@ -0,0 +1,182 @@
+const ts = require("typescript");
+const fs = require("fs");
+const path = require("path");
+
+/**
+ * Writes the result of smooshing to a file
+ */
+function smoosh(base) {
+  const smooshedSrc = returnSmooshed(base);
+  const outputFile = `./${base}.tsx`;
+  fs.writeFileSync(outputFile, smooshedSrc);
+}
+
+const declDoesntExist = { typeAliases: [], declarations: [], imports: [] };
+
+function returnSmooshed(base) {
+  const dtsFile = `${base}.d.ts`;
+  // TODO(btford): log a warning here?
+  const decls = fs.existsSync(dtsFile) ? parseDts(dtsFile) : declDoesntExist;
+
+  const jsFile = `${base}.js`;
+  const enrichedJsNode = enrichJs(jsFile, decls);
+
+  const outputFile = `${base}.tsx`;
+
+  const resultFile = ts.createSourceFile(
+    outputFile,
+    "",
+    ts.ScriptTarget.Latest,
+    false,
+    ts.ScriptKind.TSX
+  );
+  const printer = ts.createPrinter({ newLine: ts.NewLineKind.LineFeed });
+
+  const smooshedSrc = printer.printNode(
+    ts.EmitHint.Unspecified,
+    enrichedJsNode,
+    resultFile
+  );
+
+  return smooshedSrc;
+}
+
+function parseDts(dtsFile) {
+  const parsed = ts.createSourceFile(
+    dtsFile,
+    fs.readFileSync(dtsFile, "utf8"),
+    ts.ScriptTarget.Latest
+  );
+
+  // these are going on top
+  const typeAliases = [];
+  const declarations = {};
+  const imports = [];
+
+  const aggregateDecl = (statement) => {
+    // console.log(statement);
+    const kind = ts.SyntaxKind[statement.kind];
+
+    if (kind === "TypeAliasDeclaration") {
+      declarations[getIdentifierName(statement)] = statement.type;
+      typeAliases.push(statement);
+      return;
+    }
+    if (kind === "ImportDeclaration") {
+      return console.log("import...");
+    }
+
+    if (kind === "FirstStatement") {
+      return statement.declarationList.declarations.map(aggregateDecl);
+    }
+
+    if (!kind.endsWith("Declaration")) {
+      const message = `Unexpected statement kind "${kind}" in type definition file "${dtsFile}"`;
+      return console.warn(message);
+    } else {
+      declarations[getIdentifierName(statement)] = statement;
+    }
+  };
+
+  parsed.statements.forEach(aggregateDecl);
+
+  return { typeAliases, declarations, imports };
+}
+
+function enrichJs(jsFile, dts) {
+  const parsed = ts.createSourceFile(
+    jsFile,
+    fs.readFileSync(jsFile, "utf8"),
+    ts.ScriptTarget.Latest
+  );
+
+  const findSource = (node) => {
+
+    let typeSource = null;
+
+    // First, search for a jsdoc tag with the type, like:
+    // @type {typeof import('./b').Noop}
+    if (node.jsDoc) {
+      const typeTag = node.jsDoc[0].tags.find(
+        (tag) => tag.tagName.escapedText === "type"
+      );
+      if (typeTag) {
+        const fileName =
+          typeTag.typeExpression.type.argument.literal.text;
+        const identifier =
+          typeTag.typeExpression.type.qualifier.escapedText;
+        const dir = path.dirname(jsFile);
+        const fullPath = path.resolve(dir, fileName + ".d.ts");
+        const importedDts = parseDts(fullPath);
+        const importedType = importedDts.declarations[identifier];
+        if (!importedType) {
+          console.warn(
+            `Could not find ${identifier} in ${fullPath} while trying to smoosh ${jsFile}`
+          );
+          return node;
+        }
+        typeSource = importedType;
+      }
+    }
+
+    // Second, use the d.ts file with the same name as this file.
+    if (!typeSource) {
+      typeSource = dts.declarations[getIdentifierName(node)];
+    }
+
+    return typeSource;
+  }
+
+  const transformer = (context) => (rootNode) => {
+    function visit(node) {
+      const kind = ts.SyntaxKind[node.kind];
+      if (kind.endsWith("Declaration")) {
+        if (kind === "FunctionDeclaration") {
+          const typeSource = findSource(node);
+          if (typeSource) {
+            return ts.factory.updateFunctionDeclaration(
+              node,
+              node.decorators,
+              node.modifiers,
+              node.asteriskToken,
+              node.name,
+              typeSource.typeParameters,
+              typeSource.parameters,
+              typeSource.type,
+              node.body
+            );
+          }
+          return node;
+        } else if (kind === 'VariableDeclaration') {
+          const typeSource = findSource(node);
+          if (typeSource) {
+            return ts.factory.updateVariableDeclaration(
+              node,
+              node.name,
+              node.exclamationToken,
+              typeSource.type,
+              node.initializer
+            );
+          }
+          return node;
+        }
+
+        return node;
+      }
+
+      return ts.visitEachChild(node, visit, context);
+    }
+    return ts.visitNode(rootNode, visit);
+  };
+
+  return ts.transform(parsed, [transformer]).transformed[0];
+}
+
+function getIdentifierName(node) {
+  return node.name.escapedText;
+}
+
+module.exports = {
+  smoosh,
+  returnSmooshed,
+};
diff --git a/scripts/ts-smoosh/test.js b/scripts/ts-smoosh/test.js
new file mode 100644
index 0000000000..72789a9f05
--- /dev/null
+++ b/scripts/ts-smoosh/test.js
@@ -0,0 +1,27 @@
+const fs = require("fs");
+const assert = require("assert").strict;
+const path = require("path");
+
+const { returnSmooshed } = require("./smoosh");
+
+const args = process.argv.slice(2);
+
+const dirs = args.length > 0 ? args : fs.readdirSync("./tests").map(f => `./tests/${f}`);
+
+dirs.forEach((dir) => {
+  const files = fs.readdirSync(dir);
+
+  files
+    .filter((file) => file.endsWith(".js"))
+    .map((file) => file.substr(0, file.length - 3))
+    .forEach((file) => {
+      const fullFile = path.resolve(dir, file);
+      console.log(`Testing ${fullFile}.js`);
+      const smooshed = returnSmooshed(fullFile);
+
+      const target = fs.readFileSync(fullFile + ".tsx", "utf8");
+      assert.equal(smooshed, target);
+    });
+});
+
+console.log("Done");
diff --git a/scripts/ts-smoosh/tests/01-functions/a.d.ts b/scripts/ts-smoosh/tests/01-functions/a.d.ts
new file mode 100644
index 0000000000..4cc6c20337
--- /dev/null
+++ b/scripts/ts-smoosh/tests/01-functions/a.d.ts
@@ -0,0 +1,6 @@
+export function foo(
+  bar: string,
+  baz: number
+): {boo: number};
+
+export function typeParams<A, B>(a: A, b: B): B;
diff --git a/scripts/ts-smoosh/tests/01-functions/a.js b/scripts/ts-smoosh/tests/01-functions/a.js
new file mode 100644
index 0000000000..65cccbb1d6
--- /dev/null
+++ b/scripts/ts-smoosh/tests/01-functions/a.js
@@ -0,0 +1,15 @@
+/**
+ * A function with a JSDoc type import that matches its name
+ * @type {typeof import('./a').foo}
+ */
+ export function foo(
+  bar,
+  baz
+)  {
+  return {boo: baz}
+}
+
+// A function with no type import
+export function typeParams(a, b) {
+  return a + b;
+}
diff --git a/scripts/ts-smoosh/tests/01-functions/a.tsx b/scripts/ts-smoosh/tests/01-functions/a.tsx
new file mode 100644
index 0000000000..168cf84717
--- /dev/null
+++ b/scripts/ts-smoosh/tests/01-functions/a.tsx
@@ -0,0 +1,13 @@
+/**
+ * A function with a JSDoc type import that matches its name
+ * @type {typeof import('./a').foo}
+ */
+export function foo(bar: string, baz: number): {
+    boo: number;
+} {
+    return { boo: baz };
+}
+// A function with no type import
+export function typeParams<A, B>(a: A, b: B): B {
+    return a + b;
+}
diff --git a/scripts/ts-smoosh/tests/02-imports/b.d.ts b/scripts/ts-smoosh/tests/02-imports/b.d.ts
new file mode 100644
index 0000000000..38ca8b3eaa
--- /dev/null
+++ b/scripts/ts-smoosh/tests/02-imports/b.d.ts
@@ -0,0 +1,2 @@
+
+export type MyFn = (a: number, b: number) => number
diff --git a/scripts/ts-smoosh/tests/02-imports/c.js b/scripts/ts-smoosh/tests/02-imports/c.js
new file mode 100644
index 0000000000..396b6c2008
--- /dev/null
+++ b/scripts/ts-smoosh/tests/02-imports/c.js
@@ -0,0 +1,9 @@
+
+/**
+ * A function with a JSDoc type import that is different from its name
+ * @type {typeof import('./b').MyFn}
+ */
+function c(a, b) {
+  console.log('haha hi')
+  return a + b;
+}
diff --git a/scripts/ts-smoosh/tests/02-imports/c.tsx b/scripts/ts-smoosh/tests/02-imports/c.tsx
new file mode 100644
index 0000000000..674be451ae
--- /dev/null
+++ b/scripts/ts-smoosh/tests/02-imports/c.tsx
@@ -0,0 +1,8 @@
+/**
+ * A function with a JSDoc type import that is different from its name
+ * @type {typeof import('./b').MyFn}
+ */
+function c(a: number, b: number): number {
+    console.log("haha hi");
+    return a + b;
+}
diff --git a/scripts/ts-smoosh/tests/03-const/e.d.ts b/scripts/ts-smoosh/tests/03-const/e.d.ts
new file mode 100644
index 0000000000..f46e533529
--- /dev/null
+++ b/scripts/ts-smoosh/tests/03-const/e.d.ts
@@ -0,0 +1,4 @@
+// hi
+export const x: number;
+
+export const add: (a: number, b: number) => number;
diff --git a/scripts/ts-smoosh/tests/03-const/e.js b/scripts/ts-smoosh/tests/03-const/e.js
new file mode 100644
index 0000000000..d0ab5ccc16
--- /dev/null
+++ b/scripts/ts-smoosh/tests/03-const/e.js
@@ -0,0 +1,3 @@
+export const x = 3;
+
+export const add = (a, b) => a + b;
diff --git a/scripts/ts-smoosh/tests/03-const/e.tsx b/scripts/ts-smoosh/tests/03-const/e.tsx
new file mode 100644
index 0000000000..8886106ea2
--- /dev/null
+++ b/scripts/ts-smoosh/tests/03-const/e.tsx
@@ -0,0 +1,2 @@
+export const x: number = 3;
+export const add: (a: number, b: number) => number = (a, b) => a + b;