# Math.floor()

The `Math.floor()` static method always rounds down and returns the largest integer less than or equal to a given number.

## Syntax

js
``````Math.floor(x)
``````

`x`

A number.

### Return value

The largest integer smaller than or equal to `x`. It's the same value as `-Math.ceil(-x)`.

## Description

Because `floor()` is a static method of `Math`, you always use it as `Math.floor()`, rather than as a method of a `Math` object you created (`Math` is not a constructor).

## Examples

### Using Math.floor()

js
``````Math.floor(-Infinity); // -Infinity
Math.floor(-45.95); // -46
Math.floor(-45.05); // -46
Math.floor(-0); // -0
Math.floor(0); // 0
Math.floor(4); // 4
Math.floor(45.05); // 45
Math.floor(45.95); // 45
Math.floor(Infinity); // Infinity
``````

In this example, we implement a method called `decimalAdjust()` that is an enhancement method of `Math.floor()`, `Math.ceil()`, and `Math.round()`. While the three `Math` functions always adjust the input to the units digit, `decimalAdjust` accepts an `exp` parameter that specifies the number of digits to the left of the decimal point to which the number should be adjusted. For example, `-1` means it would leave one digit after the decimal point (as in "× 10-1"). In addition, it allows you to select the means of adjustment — `round`, `floor`, or `ceil` — through the `type` parameter.

It does so by multiplying the number by a power of 10, then rounding the result to the nearest integer, then dividing by the power of 10. To better preserve precision, it takes advantage of Number's `toString()` method, which represents large or small numbers in scientific notation (like `6.02e23`).

js
``````/**
* Adjusts a number to the specified digit.
*
* @param {"round" | "floor" | "ceil"} type The type of adjustment.
* @param {number} value The number.
* @param {number} exp The exponent (the 10 logarithm of the adjustment base).
* @returns {number} The adjusted value.
*/
function decimalAdjust(type, value, exp) {
type = String(type);
if (!["round", "floor", "ceil"].includes(type)) {
throw new TypeError(
"The type of decimal adjustment must be one of 'round', 'floor', or 'ceil'.",
);
}
exp = Number(exp);
value = Number(value);
if (exp % 1 !== 0 || Number.isNaN(value)) {
return NaN;
} else if (exp === 0) {
return Math[type](value);
}
const [magnitude, exponent = 0] = value.toString().split("e");
const adjustedValue = Math[type](`\${magnitude}e\${exponent - exp}`);
// Shift back
const [newMagnitude, newExponent = 0] = adjustedValue.toString().split("e");
return Number(`\${newMagnitude}e\${+newExponent + exp}`);
}

// Decimal round
const round10 = (value, exp) => decimalAdjust("round", value, exp);
// Decimal floor
const floor10 = (value, exp) => decimalAdjust("floor", value, exp);
// Decimal ceil
const ceil10 = (value, exp) => decimalAdjust("ceil", value, exp);

// Round
round10(55.55, -1); // 55.6
round10(55.549, -1); // 55.5
round10(55, 1); // 60
round10(54.9, 1); // 50
round10(-55.55, -1); // -55.5
round10(-55.551, -1); // -55.6
round10(-55, 1); // -50
round10(-55.1, 1); // -60
// Floor
floor10(55.59, -1); // 55.5
floor10(59, 1); // 50
floor10(-55.51, -1); // -55.6
floor10(-51, 1); // -60
// Ceil
ceil10(55.51, -1); // 55.6
ceil10(51, 1); // 60
ceil10(-55.59, -1); // -55.5
ceil10(-59, 1); // -50
``````

## Specifications

Specification
ECMAScript Language Specification
# sec-math.floor

## Browser compatibility

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