JavaScript2Java Bridge permits to expose Java objects to JavaScript. As JavaScript is weakly typed, it doesn't care about types of assigned value and vairable which the value is assigned to during the assignment. Java, however, cannot allow this.
Currently, when a value is assigned to a variable of incompatible type, a variable ends up with its original value changed to something meaningless (MIN_VALUE in case of integer), and no error is reported.
Consider the following example with integer:
WebEngine e; // Initialized somehow
MyObject o = new MyObject(); // Has an integer field
o.integerField = 3;
e.addJavaScriptBinding("test", o);
e.executeScript("test.integerField='tralala'"); // We assign string to integer field here, and JS sees no problem
System.out.println(o.integerField); // o.integerField is now Integer.MIN_VALUE
In my opinion, this situation should be reported (by throwing an exception, for example), and original value of a variable should not be damaged.