Decide whether the value is really a number
An account identifier may contain only digits while still being a label rather than a quantity. If nobody should add or multiply it, a string is often a better contract. That choice also preserves leading zeros and avoids numeric formatting surprises. Choose the representation at the API boundary instead of trying to repair precision after a table already contains rounded values.
Understand the safe-integer boundary
Ordinary JavaScript numbers use floating-point representation. Integer values are considered safe only within the range from negative 9,007,199,254,740,991 to positive 9,007,199,254,740,991. Number.isSafeInteger checks both the integer requirement and that range. Being a finite number or an integer does not by itself prove that neighboring large integers can still be distinguished reliably.
Follow an identifier through a workflow
Imagine a CSV import with a record identifier longer than sixteen digits. Keep the field as text when parsing, editing, filtering and exporting it. Do not convert it with Number merely because a form input looks numeric. A search for that identifier must compare its exact string representation, otherwise two distinct external records could appear to refer to the same row.
Use BigInt when arithmetic is required
BigInt can represent integer quantities beyond the safe Number range, but it has different interoperability rules. Do not casually mix it with Number arithmetic. Decide how it travels across JSON and database boundaries, usually through an explicit string representation and conversion rule. It also does not solve arbitrary decimal arithmetic, which requires a separate representation and rounding policy.
Validate before losing information
Checking Number.isSafeInteger after a value has already been rounded cannot recover the original digits. Validate the source string and preserve it until the correct conversion is known. A JSON producer can send an identifier as a quoted string rather than an oversized numeric literal. Document this contract so a future backend or export change does not silently reintroduce the issue.
Verify neighboring and formatted inputs
Test leading zeros, the safe-range boundary, a value beyond it and two large neighboring identifiers. Check form submission, JSON round-trips and spreadsheet export separately. Confirm that the displayed text exactly matches the source and that sorting uses the intended rule. A correct first screen is insufficient if a later download changes the identifier that another system depends on.
Further reading
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