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When encountering the “illegal argument in isolate message: object is unsendable” error in an isolate,
it typically means you are attempting to send an object that cannot be transferred across isolates using the isolate ports or messages.
This error occurs when working with web workers or other related technologies that make use of isolates.
Isolates are separate threads of execution that do not share memory, and they communicate with each other using messages.
To transfer data or objects between isolates, they must be serializable, which means they can be converted into a stream of bytes.
Not all JavaScript objects are serializable, and attempting to send non-serializable objects will result in the mentioned error.
To better understand this, let’s consider an example. Imagine you have two isolates, isolateA and isolateB, and you want to send an object from isolateA to isolateB:
// Isolate A
const obj = {
name: "John",
age: 25
};
isolateB.postMessage(obj); // Sending the object from Isolate A to Isolate B
In this example, if the object obj contains only serializable data (like strings, numbers, booleans, or other serializable objects), the message will be successfully sent without any errors.
However, if obj contains non-serializable data like functions, DOM elements, or references to objects that are specific to the isolate’s memory, then an “illegal argument in isolate message: object is unsendable” error will be thrown.
// Isolate A
const obj = {
name: "John",
age: 25,
sayHello: function() {
console.log("Hello!");
}
};
isolateB.postMessage(obj); // Error: illegal argument in isolate message: object is unsendable
In the above example, the function sayHello inside the object obj is not serializable, resulting in the error.
To fix this issue, you need to ensure that the data you want to send is serializable.
If you need to transfer non-serializable objects between isolates, you have to find alternative solutions.
One possible solution is to send only the required data within the object and recreate the object with the necessary references or functions in the receiving isolate.
// Isolate A
const obj = {
name: "John",
age: 25
};
// Sending only the required data
isolateB.postMessage(obj.name); // Only sending the name property
In isolateB, you can create a new object using the received data and add any required functions or references manually.
// Isolate B
isolateB.onmessage = function(event) {
const name = event.data;
const obj = {
name: name,
sayHello: function() {
console.log("Hello, " + this.name + "!")
}
};
obj.sayHello(); // Output: Hello, John!
};
By restructuring the sent data and manually recreating the object in the receiving isolate, you can overcome the “illegal argument in isolate message: object is unsendable” error.