UglifyJS/test/compress/arrays.js

holes_and_undefined: {
    input: {
        w = [1,,];
        x = [1, 2, undefined];
        y = [1, , 2, ];
        z = [1, undefined, 3];
    }
    expect: {
        w=[1,,];
        x=[1,2,void 0];
        y=[1,,2];
        z=[1,void 0,3];
    }
}
Fix output for arrays containing undefined values. 1b6bcca7 was a first attempt at this. That commit made Uglify stop replacing holes with undefined, but instead it started replacing undefined with holes. This is slightly problematic, because there is a difference between a hole and an undefined value. More problematically, it changed [1,undefined] to [1,] which generally doesn't even parse as a hole (just as a trailing comma), so it didn't even preserve the length of the array! Instead, parse holes as their own special AST node which prints invisibly. 2013-01-16 19:59:19 +00:00			`holes_and_undefined: {`
			`input: {`
Fix output for arrays whose last element is a hole: [1,,] 1529ab96 started to do this (by considering holes to be separate from "undefined") but it still converted [1,,] (length 2, last element hole, trailing comma) to [1,] (length 1, trailing comma) Unfortunately the test suite doesn't really make this clear: the new test here passes with or without this patch because run-tests.js beautifys the expected output (in "make_code"), which does the incorrect transformation! If you make some manual change to arrays.js to make the test fail and see the INPUT and OUTPUT, then you can see that without this fix, [1,,] -> [1,], and with this fix it stays [1,,]. 2013-01-16 19:59:19 +00:00			`w = [1,,];`
Fix output for arrays containing undefined values. 1b6bcca7 was a first attempt at this. That commit made Uglify stop replacing holes with undefined, but instead it started replacing undefined with holes. This is slightly problematic, because there is a difference between a hole and an undefined value. More problematically, it changed [1,undefined] to [1,] which generally doesn't even parse as a hole (just as a trailing comma), so it didn't even preserve the length of the array! Instead, parse holes as their own special AST node which prints invisibly. 2013-01-16 19:59:19 +00:00			`x = [1, 2, undefined];`
			`y = [1, , 2, ];`
			`z = [1, undefined, 3];`
			`}`
			`expect: {`
Fix output for arrays whose last element is a hole: [1,,] 1529ab96 started to do this (by considering holes to be separate from "undefined") but it still converted [1,,] (length 2, last element hole, trailing comma) to [1,] (length 1, trailing comma) Unfortunately the test suite doesn't really make this clear: the new test here passes with or without this patch because run-tests.js beautifys the expected output (in "make_code"), which does the incorrect transformation! If you make some manual change to arrays.js to make the test fail and see the INPUT and OUTPUT, then you can see that without this fix, [1,,] -> [1,], and with this fix it stays [1,,]. 2013-01-16 19:59:19 +00:00			`w=[1,,];`
Fix output for arrays containing undefined values. 1b6bcca7 was a first attempt at this. That commit made Uglify stop replacing holes with undefined, but instead it started replacing undefined with holes. This is slightly problematic, because there is a difference between a hole and an undefined value. More problematically, it changed [1,undefined] to [1,] which generally doesn't even parse as a hole (just as a trailing comma), so it didn't even preserve the length of the array! Instead, parse holes as their own special AST node which prints invisibly. 2013-01-16 19:59:19 +00:00			`x=[1,2,void 0];`
			`y=[1,,2];`
			`z=[1,void 0,3];`
			`}`
			`}`