Question

I’m creating a GWT version of a Java library which has support for the javax.script.ScriptEngine to evaluate functions dynamically via Javascript, e.g.,

o => o % 2 == 0

where at runtime, the value of “o” is defined via the javax.script.Bindings (the o => part is stripped of course).

The problem is, how can I get the same effect from within GWT? I use a native function

native Object nativeEval(String script) /*-{
    return $wnd.eval(script);
}-*/

nativeEval("o % 2 == 0");

But how can I bind a value to the identifier “o”?

Answer 1

new Function("o", "return (" + expressionThatUsesO + ")")(o)

If expressionThatUsesO is "o % 2" then this is equivalent to a global function that is immediately called

(function (o) { return o % 2; })(o)

For reference, https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Function :

new Function ([arg1[, arg2[, ... argN]],] functionBody)

Parameters

arg1, arg2, ... argN

Names to be used by the function as formal argument names. Each must be a string that corresponds to a valid JavaScript identifier or a list of such strings separated with a comma; for example "x", "theValue", or "a,b".

functionBody

A string containing the JavaScript statements comprising the function definition.