Can uglify-js remove the console.log statements?

Question

I'm using uglify-js to minify the source code. I want to remove the console.log statements of the original source code. Is it possible? Or is there any other compressor tool supports this?

I use the code as below in Node.js.

var uglify = require('uglify-js'); var originalSourceCode = 'var name = function(){var str = "test"; return str}; console.log("log data");'; var minifiedCode = uglify.minify(originalSourceCode, {                 fromString : true,                 mangle: {},                 warnings: true             }); console.log(minifiedCode); 

The output is:

$node m.js { code: 'var name=function(){var a="test";return a};console.log("log data");',   map: 'null' } 

In the minified code the console.log isn't removed.

Answer 1

There's also another option called drop_console which has been added recently (late 2013)

drop_console -- default false. Pass true to discard calls to console.* functions 

This is added to the grunt init config like this:

grunt.initConfig({   uglify: {     options: {       compress: {         drop_console: true // <-       }     },     my_target: {       files: {         'dest/output.min.js': ['src/input.js']       }     }   } }); 

As taken from the grunt-contrib-uglify github documents

Answer 2

In the lastest uglify-js ( v2.4.3), a new compress option ‘pure_funcs’ is added. If I add the console.log functions to this array, it will be removed in the minified js file. The test code below shows how this option works. This is exactly what I want.

// file: m.js var uglify = require('uglify-js'); var originalSourceCode = 'var name = function(){var str = "test"; return str}; console.log("log data" + name());'; var minifiedCode = uglify.minify(originalSourceCode, {                 fromString : true,                 mangle: {},                 warnings: true,                 compress:{                     pure_funcs: [ 'console.log' ]                 }             }); console.log(minifiedCode);  $node m.js WARN: Dropping side-effect-free statement [?:1,53] { code: 'var name=function(){var n="test";return n};',   map: 'null' } 

Quotes from https://github.com/mishoo/UglifyJS2

pure_funcs -- default null. You can pass an array of names and UglifyJS will assume that those functions do not produce side effects. DANGER: will not check if the name is redefined in scope. An example case here, for instance var q = Math.floor(a/b). If variable q is not used elsewhere, UglifyJS will drop it, but will still keep the Math.floor(a/b), not knowing what it does. You can pass pure_funcs: [ 'Math.floor' ] to let it know that this function won't produce any side effect, in which case the whole statement would get discarded. The current implementation adds some overhead (compression will be slower).