This is useful while compressing generated code; for example compressing JS
compiled by CoffeeScript (assuming you got a source map):
uglifyjs2 --in-source-map generated.js.map \
--source-map uglified.js.map \
-o uglified.js
The above assumes you have a "generated.js.map" file which is the source
mapping between your CoffeeScript and the generated.js (compiled output from
CoffeeScript). The name of the input file is not present in this example;
it will be fetched from the source map (but it can be passed manually too).
The output will be in "uglified.js" and the output map "uglified.js.map"
will actually map to the original CoffeeScript code, rather than to
generated.js.
if undefined is defined, ;-), we replace AST_Undefined nodes to a reference
to the "undefined" variable; in turn the mangler will compress it to a
single letter; this helps at least on jQuery.
- a = a + x ==> a+=x
- joining consecutive var statements (hoisting is not always desirable)
- x == false ==> x == 0, x != true ==> x != 1
- x, x ==> x; x = exp(), x ==> x = exp()
- discarding useless break-s
- do multiple passes in tighten_body if it was changed
- transform if (foo) return x; return y; ==> return foo?x:y
- don't optimize !0 as true (use best_of after evaluation of constant expr)
With hoist_vars off we now beat UglifyJS v1 on jQuery-1.8.1
- all symbols now have a `thedef` property which is a SymbolDef object,
instead of the `uniq` that we had before (pointing to the first occurrence
of the name as declaration).
- for undeclared symbols we still create a SymbolDef object in the toplevel
scope but mark it "undeclared"
- we can now call figure_out_scope after squeezing, which is useful in order
not to mangle names that were dropped by the squeezer
The following nodes were instances of AST_BlockStatement: AST_Scope,
AST_SwitchBlock, AST_SwitchBranch. Also, AST_Try, AST_Catch, AST_Finally
were having a body instanceof AST_BlockStatement.
Overloading the meaning of AST_BlockStatement this way turned out to be a
mess; we now have an AST_Block class that is the base class for things
having a block of statements (might or might not be bracketed). The
`this.body` of AST_Scope, AST_Try, AST_Catch, AST_Finally is now an array of
statements (as they inherit from AST_Block).
Avoiding calling superclass's _walk function in walkers (turns out we walked
a node multiple times).
optimize away while(false), and transform while(true) ==> for(;;).
UNSAFE:
some expressions are optimized away when we're in boolean context and can
determine that the value will always be true or false. For example:
x() || true ==> always `true` in boolean context
x() && false ==> always `false` in boolean context
It's not technically correct to drop these expressions since we drop the
function call too (that might have side effects); on the other hand, I can't
see any legitimate use for such expressions and they might simply indicate a
bug (we do warn about it).
if (foo) {
with (bar)
if (baz)
x();
} else y();
(the compressor removes the brackets since the consequent consists of a
single statement, but the codegen must include the brackets because
otherwise the `else` would refer to the inner `if`)
the statements if, for, do, while and with might have an AST_EmptyStatement
as body; if that's the case, we need to make sure that the semicolon gets in
the output.
- added walker for AST_ObjectProperty
- handle redefinitions properly (only mangle one symbol, make them all point
to a single definition)
DynarchLIB seems to run fine after mangling + compressed output.
who would have thought that str.charAt(str.length - 1) is not a constant,
instant operation? seems to get slower and slower as the string grows.
0.6s vs. 3s
