Uglifyjs: [ES6] Property mangling breaks destructuring

[AshleyScirra]

Input:

let o = {
    foo: "foo",
    bar: "bar"
};

let {foo, bar} = o;

Output with --mangle-props=1 --beautify:

let o = {
    a: "foo",
    b: "bar"
};

let {foo,  bar} = o; // oops - both are assigned undefined

The syntax let {foo, bar} = o needs to consider foo and bar as candidates for property mangling since they implicitly read object properties. This probably needs special consideration to avoid colliding with other local variable names.

[kzc]

The harmony branch is a work in progress and has known problems related to mangling. It's advisable to disable mangle and compress for the time being.

Could you please put an [ES6] prefix in this issue title?

[avdg]

In few days I guess I can start looking in these kinds of issues without internet trouble.

[avdg]

See #1286. Should work fine with 'unused' (a compression option) disabled. And there is a proposed fix there as well, though some additional testing is still welcome.

[avdg]

Is still an issue?

[alexlamsl]

@avdg no idea - can you reproduce the results with the command line as specified in https://github.com/mishoo/UglifyJS2/issues/1315#issue-180924062 on harmony?

If not, then I'll close this.

[avdg]

https://avdg.github.io/uglify/#ref_harmony-editor_let_s0o_s0_x3d_s0_x7b_r_n_s3foo_x3a_s0_x22foo_x22_x2c_r_n_s3bar_x3a_s0_x22bar_x22_r_n_x7d_x3b_r_n_r_nlet_s0_x7bfoo_x2c_s0bar_x7d_s0_x3d_s0o_x3b-bool_beautify0

[alexlamsl]

I've got SCRIPT5009: 'Promise' is undefined so I don't think the linked page works for me at all.

[avdg]

oh, something I can't use I guess...

[avdg]

is that on a recent browser?

[alexlamsl]

IE11 on Win10, so it's as recent as I can get my hands on.

[avdg]

oh, yeah, I see that... You should be fine with edge though... at least if you want to be a daredevil :-)

[alexlamsl]

Edge is not available for the Stable Branch - and for good reasons :wink:

[avdg]

uh I will look for a fallback library I guess :-)

[avdg]

@alexlamsl I've implemented support for ie 11 on my online uglify editor. Enjoy :-)

[kzc]

The bug at the top of this ticket appears to have been addressed:

$ bin/uglifyjs -V
uglify-es 3.0.12

$ cat 1315.js 

    let o = {
        foo: "foo",
        bar: "bar"
    };
    let {foo, bar} = o;
    console.log(foo, bar);



md5-7c09a15dae0cf9d30faa396a937ea1bc



$ node 1315.js
foo bar



md5-7c09a15dae0cf9d30faa396a937ea1bc



$ bin/uglifyjs 1315.js --mangle-props | node
foo bar

$ bin/uglifyjs 1315.js --mangle-props
let o={o:"foo",l:"bar"};let{o:foo,l:bar}=o;console.log(foo,bar);



md5-7c09a15dae0cf9d30faa396a937ea1bc



$ bin/uglifyjs 1315.js --mangle-props -c -m --toplevel | node
foo bar

$ bin/uglifyjs 1315.js --mangle-props -c -m --toplevel
let o={o:"foo",l:"bar"},{o:a,l:b}=o;console.log(a,b);

[alexlamsl]

Good to be looking after self-healing software :angel:

[kzc]

Fixed by https://github.com/mishoo/UglifyJS2/commit/7bcb442e4ce548de2e6258792146aadb5bc24034