Number.prototype.toExponential() formats a number as an exponential (scientific) string (same API as MDN Number.toExponential). Optional fractionDigits controls digits after the decimal. This tutorial covers syntax, special values, comparisons, five examples, and try-it labs.
toExponential(digits)
d.dddde±e
0 to 100
As needed
parseFloat
Everywhere
Huge and tiny numbers are hard to read as plain decimals. Scientific notation writes them as a short mantissa times a power of ten — for example 1.23 × 105. In JavaScript that looks like "1.23e+5".
toExponential() builds that string for you. Use it for logs, science UIs, charts, and any place where a consistent exponential layout beats a long digit run.
This page is part of JavaScript Number Methods. Related formatters include toString(), toFixed(), and toPrecision().
toExponential() MethodCall number.toExponential() or number.toExponential(fractionDigits) on a number primitive or Number object. You always get a string; the number itself does not change.
The result has one digit before the decimal point (unless the number is zero), then an e+ or e- exponent. Negative numbers keep a leading -.
Integer literals need parentheses or a space before the dot: (77).toExponential() or 77 .toExponential(). Otherwise 77.toExponential looks like a decimal to the parser.
General form of Number.prototype.toExponential:
number.toExponential()
number.toExponential(fractionDigits)Always a string in exponential notation. Special cases:
| Value | Returns (example) |
|---|---|
| Normal number | (77.1234).toExponential() → "7.71234e+1" |
| With digits | (77.1234).toExponential(2) → "7.71e+1" |
| Negative number | (-6.5e6).toExponential() → "-6.5e+6" |
| Tiny magnitude | (0.0000123).toExponential() → "1.23e-5" |
0 / -0 | "0e+0" (sign of -0 may appear as "-0e+0") |
Infinity | "Infinity" |
NaN | "NaN" |
fractionDigits < 0 or > 100.this value (for example a plain object).(77.1234).toExponential(); // "7.71234e+1"
(77.1234).toExponential(2); // "7.71e+1"
(123456).toExponential(2); // "1.23e+5"
(-6.5e6).toExponential(); // "-6.5e+6"
Number.parseFloat("123e-2").toExponential(1); // "1.2e+0"| Goal | Code |
|---|---|
| Full exponential string | n.toExponential() |
| 2 digits after decimal | n.toExponential(2) |
| Large integer, short form | (123456).toExponential(2) |
| Very small number | (1.23e-5).toExponential() |
| Parse exponential text | Number.parseFloat("1.23e+5") |
| Fixed decimals (not expo) | n.toFixed(2) |
Four facts to remember about Number.prototype.toExponential().
stringThe number is never changed
0–100Optional fractionDigits range
e±Always scientific notation
BaselineWorks in all modern engines
toExponential() vs toFixed() vs toPrecision()toExponential(d) | toFixed(d) | toPrecision(p) | |
|---|---|---|---|
| Main job | Always scientific form | Fixed decimal places | Significant digits |
| Example for 1234.5 | "1.23e+3" (d=2) | "1234.50" (d=2) | May be plain or expo |
| Best for | Science / huge & tiny values | Currency / UI decimals | Controlled precision display |
Examples follow MDN patterns. Use View Output or Try It Yourself for each case.
Default call, then control fraction digits.
Omit the argument to keep as many digits as needed.
(77.1234).toExponential(); // "7.71234e+1"77.1234 becomes one digit before the point (7), then the rest of the significand, then e+1 because the value is about 7.71 × 101.
Pass 2 to round to two digits after the decimal in the mantissa.
(77.1234).toExponential(2); // "7.71e+1"The engine rounds the mantissa to two fractional digits. Try (4) to get "7.7123e+1".
Large values, tiny values, and parsing back.
Compress a big integer into a short scientific string.
(123456).toExponential(2); // "1.23e+5"123456 is about 1.23 × 105, so the exponent is +5.
Very small magnitudes use a negative exponent.
(0.0000123).toExponential(); // "1.23e-5"Moving the decimal five places right gives 1.23, so the exponent is -5.
Build an exponential string from a parsed value — an MDN-style round trip.
Number.parseFloat("123e-2").toExponential(1); // "1.2e+0""123e-2" parses to 1.23. Formatting with one fraction digit yields "1.2e+0".
toFixed or a decimal library for currency.toExponential() Builds the StringMust be a Number primitive or wrapper.
One digit before the decimal; pick the exponent.
Round or expand digits after the point (0–100).
Form like "1.23e+5"; original number unchanged.
fractionDigits outside 0–100 throws RangeError.toPrecision, which may stay plain).Infinity and NaN return "Infinity" / "NaN", not expo strings.toLocaleString() with suitable options — not toExponential.Number.prototype.toExponential() is Baseline Widely available — part of JavaScript since early ECMAScript editions and supported in every modern browser and Node.js.
Safe for production everywhere. Optional fractionDigits 0–100 works consistently across engines.
Bottom line: Use freely for scientific display. Prefer toFixed or decimal libraries for currency and exact decimal places.
Number.prototype.toExponential() turns any number into a clear scientific string, with optional control over mantissa digits. It is ideal for logs, science UIs, and values that span many orders of magnitude.
Continue with toFixed() for fixed decimals, toString() for base conversion, or return to the Number methods hub.
(123456).toExponential(2)fractionDigits for readable charts and labelsNumber.parseFloat when you need the value againtoFixed when you need plain fixed decimals10.toExponential() without space/parens (syntax error)-0 the same waytoExponential with toPrecision (different goals)Number.toExponential()Format numbers in scientific notation with optional digit control.
string
API0–100
ParamAlways expo
ShapeKept
NegativesBaseline
SupportIn JavaScript source code you can also write numbers with exponents directly — 1.23e5 is the same value as 123000. toExponential() is the reverse direction: number → that style of text.
Return to the hub for the growing Number.prototype collection.
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