Pull the error object out of isolated-vm when a user script throws an error.

packages/server/src/jsRunner/tests/jsRunner.spec.ts

@@ -44,7 +44,7 @@ describe("jsRunner (using isolated-vm)", () => {
     const output = await processJS(
       `return this.constructor.constructor("return process.env")()`
     )
-    expect(output).toBe("Error while executing JS")
+    expect(output).toBe("ReferenceError: process is not defined")
   })
 
   describe("helpers", () => {

packages/server/src/jsRunner/vm/isolated-vm.ts

@@ -17,6 +17,15 @@ class ExecutionTimeoutError extends Error {
   }
 }
 
+class UserScriptError extends Error {
+  constructor(readonly userScriptError: Error) {
+    super(
+      `error while running user-supplied JavaScript: ${userScriptError.message}`,
+      { cause: userScriptError }
+    )
+  }
+}
+
 export class IsolatedVM implements VM {
   private isolate: ivm.Isolate
   private vm: ivm.Context
@@ -29,6 +38,7 @@ export class IsolatedVM implements VM {
 
   private readonly resultKey = "results"
   private runResultKey: string
+  private runErrorKey: string
 
   constructor({
     memoryLimit,
@@ -47,6 +57,7 @@ export class IsolatedVM implements VM {
     this.jail.setSync("global", this.jail.derefInto())
 
     this.runResultKey = crypto.randomUUID()
+    this.runErrorKey = crypto.randomUUID()
     this.addToContext({
       [this.resultKey]: { [this.runResultKey]: "" },
     })
@@ -216,7 +227,13 @@ export class IsolatedVM implements VM {
       }
     }
 
-    code = `results['${this.runResultKey}']=${this.codeWrapper(code)}`
+    code = `
+      try {
+        results['${this.runResultKey}']=${this.codeWrapper(code)}
+      } catch (e) {
+        results['${this.runErrorKey}']=e
+      }
+    `
 
     const script = this.isolate.compileScriptSync(code)
 
@@ -227,6 +244,9 @@ export class IsolatedVM implements VM {
 
     // We can't rely on the script run result as it will not work for non-transferable values
     const result = this.getFromContext(this.resultKey)
+    if (result[this.runErrorKey]) {
+      throw new UserScriptError(result[this.runErrorKey])
+    }
     return result[this.runResultKey]
   }
 

packages/string-templates/src/helpers/javascript.ts

@@ -100,6 +100,9 @@ export function processJS(handlebars: string, context: any) {
     if (error.name === "ExecutionTimeoutError") {
       return "Request JS execution limit hit"
     }
+    if ("userScriptError" in error) {
+      return error.userScriptError.toString()
+    }
     return "Error while executing JS"
   }
 }