Enable the --define and (global_defs) option to define contents of random variables.

[fabiosantoscode]

Sometimes your "debug" flag may not be a global variable, it could be a property of a global variable. So I'm sending this PR to allow --define 'globalVariable.foo.bar=false' as well as just --define globalVariable=false.

The reasoning behind building this was to support React and common React code which uses if (process.env.NODE_ENV !== "production") guards all the time for development-only code. I found some inspiration in webpack's DefinePlugin for the interface, and started implementing.

[avdg]

So this pr has also support for the squared bracket notation as well. Maybe the documentation should say that javascript style array reference is allowed instead of just saying "oh, you can do this too (but silently don't say what is fine and what is not)".

I like the idea for this pr in general though.

[kzc]

What if the define expression is on the left hand side?

$ echo 'D = 27; console.log(D);' | bin/uglifyjs --define D=5 -cm
D=27,console.log(5);

$ echo 'D.E = 27; console.log(D.E);' | bin/uglifyjs --define D.E=5 -cm
5=27,console.log(5);

Or if the define expression is referenced indirectly?

$ echo 'var d = D; console.log(D.E, d.E);' | bin/uglifyjs --define D.E=5 -cm
var d=D;console.log(5,d.E);

[avdg]

The compressor has some part of code that test if a node evaluates to a const. Maybe that code can be used to evaluate the expression. Although one can think "Why stop at constants and inject javascript while at it..."

[kzc]

The compressor has some part of code that test if a node evaluates to a const. Maybe that code can be used to evaluate the expression.

globalVariable.foo.bar would not be considered to be a constant expression, so evaluate() wouldn't be applicable here.

[kzc]

@fabiosantoscode It's good that this PR distinguishes between a local foo.bar and a global foo.bar for the code:

function f(foo) { return foo.bar; }
console.log(f({bar:3}), foo.bar);

$ echo 'function f(foo){return foo.bar;} console.log(f({bar: 3}), foo.bar);' | bin/uglifyjs --define foo.bar=5 -c | node
3 5

Could you add such a test to this PR to ensure no future regressions?

[kzc]

Here's another variation that also works correctly:

function f() {
    var foo = { bar: 2 };
    return foo.bar;
}

function g() {
    return foo.bar;
}

console.log(f(), g(), foo.bar);

$ echo 'function f(){var foo={bar:2};return foo.bar}function g(){return foo.bar}console.log(f(),g(),foo.bar);' | bin/uglifyjs --define foo.bar=5 -c | node
2 5 5

That could be added as a test as well.