Starts a new (asynchronous) JS run.

This may only throw if value of input is unknown or config cannot be supported. To verify whether a RunConfig can be supported in a forward compatible manner (i.e. when new options are added in later versions) implementations of JSEnvs must use RunConfig.Validator.

This must not throw if the run cannot be started or there is a problem with the input's content (e.g. file does not exist, syntax error, etc.). In this case, JSRun#future should be failed instead.

Like start, but initializes a communication channel.

Inside the VM this is to provide a global JavaScript object named scalajsCom that can be used to interact with the message channel. Its operations are:

// initialize com (with callback). May only be called once.
scalajsCom.init(function(msg) { console.log("Received: " + msg); });

// send a message to host system
scalajsCom.send("my message");

All messages, sent in both directions, must be valid UTF-16 strings, i.e., they must not contain any unpaired surrogate character. The behavior of a communication channel is unspecified if this requirement is not met.

We describe the expected message delivery guarantees by denoting the transmitter as t and the receiver as r. Both the JVM and the JS end act once as a transmitter and once as a receiver. These two transmitter/receiver pairs (JS/JVM and JVM/JS) are independent.

For a pair (t,r):

• If t calls JSComRun#send exactly in the sequence

send(m_1), ..., send(m_n)

and r observes onMessage(m_k) (k <= n) but not onMessage(m_{k+1}), r must observe

onMessage(m_1), ..., onMessage(m_k)

exactly in this order.

• If t and r keep running indefinitely and t sends n messages, r receives n messages.