/JavaScript

# Math.floor()

The `Math.floor()` function returns the largest integer less than or equal to a given number.

## Syntax

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

`x`

A number.

### Return value

A number representing the largest integer less than or equal to the specified number.

## 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).

Note: `Math.floor(null)` returns 0, not a `NaN`.

## Examples

### Using Math.floor()

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

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`).

```/**
* 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
```

## Browser compatibility

Desktop Mobile Server
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet Deno Node.js
`floor`
1
12
1
3
3
1
4.4
18
4
10.1
1
1.0
1.0
0.10.0