Monitor primitive String declaration

I am not sure what you mean by do "test;"; but if you want to trigger an event whenever a variable is assigned a new value, no, there is no way to trigger an event for variable changes.

If you want to watch a variable, it is better to re-design your system to make a call instead of assigning a variable. Instead of doing:

running_mode = "test";

require

switch_mode("test");

and call whatever event handlers you want to trigger on this update.

If you really want to watch the value of a global variable, you can do it by checking the value once in every turn of the main loop:

function is_mode_changed() {
   if (running_mode=="test") event_handler();
   process.nextTick(is_mode_changed);
}

Once you call this function, it will continue running once each turn of the main loop. If it what you want to do is something like following a variable to do some specific tasks time to time, like following a global counter and doing some cleanup tasks everytime counter reaches 1000, this is a good way to do. If what you want to do something immediately after a variable is changed, it is not possible.

I hope I could understand your question correctly.

UPDATE

[I am adding this in regards to the comment below which rendered everything above unrelated to question because I had misunderstood it.]

As you mentioned yourself, a string literal like "test" is a primitive value which is not an object. So, it is handled by the interpreter in a way we cannot alter.

From Ecma-262:

4.3.2 primitive value

member of one of the types Undefined, Null, Boolean, Number, or String as defined in Clause 8

NOTE: A primitive value is a datum that is represented directly at the lowest level of the language implementation.

To prevent confusion, Clause 8 is the section of standard on Types as listed above.

Since you specified V8, and not per-spec-ECMAScript, you have more concrete options at your disposal. In the V8 API there is classes/templates or primitives that are separate from those of object wrappers for primitives. In order to be able to hook in a way to know when this actually happens would likely require modifying v8 in a custom manner, but it is doable.

http://code.google.com/p/v8/source/browse/branches/bleeding_edge/include/v8.h#1017

Also much of the action takes place in js itself. Perhaps not the very constructor itself, but everything that happens thereafter. String.prototype.toString/valueOf.

http://code.google.com/p/v8/source/browse/branches/bleeding_edge/src/string.js