fix(compat): read sparse array holes as undefined in toString - #2091
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toString mapped array elements with Array.prototype.map, which skips holes in a sparse array. lodash reads every index, so a hole is rendered as 'undefined' rather than dropped: toString([1, , 3]) // es-toolkit: '1,,3' // lodash: '1,undefined,3' Iterate by index so holes are converted the same way lodash does.
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raon0211
approved these changes
Sep 8, 2026
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Summary
compat/toStringrenders an array by mapping its elements withArray.prototype.map, which skips holes in a sparse array. lodash reads every index, so a hole is converted asundefinedrather than dropped:Changes
Iterate the array by index instead of using
.map, so each hole is read asundefinedand converted through the same path as any other element. Dense arrays are unaffected, and the-0, symbol, and nested-array handling stay the same.Added tests for sparse inputs.
Verified
Ran the compat implementation against
lodashat runtime across sparse, dense, nested, nullish,-0, and symbol arrays. All outputs match.