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Use Number(text) when the entire input should represent a number. Use parseInt(text, 10) or parseFloat(text) only when you deliberately want to read an integer or decimal prefix. TypeScript does not convert a string just because you annotate or assert it as a number; conversion happens at runtime using JavaScript.
Choose the conversion method that matches your input
| What you need | Use | Behavior |
|---|---|---|
| Convert the whole string to a number | Number(text) |
Use when trailing nonnumeric text should not be accepted as part of a value. Check for NaN afterward. |
| The same general conversion in a compact expression | +text |
Unary plus explicitly coerces the value to a number. Number(text) is often easier to read, especially in beginner code. |
| Read an integer prefix | parseInt(text, 10) |
Reads an integer from the start; it can ignore trailing text and drops a fractional part. Specify radix 10 for ordinary decimal input. |
| Read a decimal prefix | parseFloat(text) |
Reads a decimal or exponent prefix and can ignore trailing text. |
Keep an integer larger than Number can represent precisely |
BigInt(text) |
Converts an integer string to a BigInt without first rounding it through Number. |
Convert a whole value with Number()
For input that is supposed to consist entirely of a numeric value, use Number():
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const value = Number("42");
Unary plus has the same general coercion intent when you want a shorter expression:
const value = +"42";
Choose this whole-value approach rather than prefix parsing when a suffix such as px should make the input invalid. The conversion can return NaN, so check its result when input may be invalid or user-supplied.
#1 Best Overall
Use parseInt() and parseFloat() only for prefixes
The parsing functions accept a valid numeric prefix rather than requiring the entire string to be numeric. That can be useful for extracting a value from a larger string, but it is not strict validation of a field.
Integer prefixes
Pass radix 10 for ordinary decimal integer input:
const pixels = parseInt("42px", 10); // 42
parseInt("1.9", 10) returns 1, and parseInt("123_456", 10) returns 123. These results illustrate why a successful parse does not prove the whole input meets a field’s requirements.
Rank #2
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Decimal prefixes
parseFloat() reads a decimal or exponent prefix:
const amount = parseFloat("3.14kg"); // 3.14
That behavior may suit extraction from a string containing a unit. If the entire field must be a valid numeric value, use a whole-value conversion and validate according to the input format you accept.
Check for NaN without rejecting zero
When conversion fails, the result may be NaN. Use Number.isNaN() to detect that result; do not use a truthiness check, because 0 is a valid numeric result.
const parsed = Number(userInput);
if (Number.isNaN(parsed)) {
throw new Error("Expected a numeric value");
}
For stricter validation, define which forms your application accepts and validate the whole input against that rule. Prefix parsers alone cannot tell you whether unexpected trailing characters should be allowed.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.TypeScript types do not convert values at runtime
TypeScript adds static checking to JavaScript, while string and number describe primitive values. An assertion such as text as number only changes how the compiler views an expression; it does not turn the underlying string into a number. Use a runtime conversion such as Number(text) instead. See the TypeScript Handbook’s Everyday Types and TypeScript for JavaScript Programmers.
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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →TypeScript 5.0 release notes show unary plus as an explicit coercion before a comparison and document compiler diagnostics for potentially implicit string-to-number coercion in relational comparisons. That compiler behavior does not make type assertions perform conversions. TypeScript 5.0 Release Notes.
Best Value
Use BigInt for very large integer strings
JavaScript’s ordinary Number type uses floating-point representation, so integers outside its precise range can lose integer precision. For a large integer that must remain exact, convert directly to BigInt rather than passing through Number or relying on parseInt.
const id = BigInt("900719925474099267");
MDN demonstrates that parsing "900719925474099267n" with parseInt() produces a rounded value and recommends BigInt("900719925474099267") for the intended BigInt value. MDN: parseInt(). For ordinary integer and decimal prefix behavior, see MDN: parseFloat().
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