Math.floor()

Math.floor() 静态方法始终向下舍入并返回小于或等于给定数字的最大整数。

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

Try it

语法

¥Syntax

js
Math.floor(x)

参数

¥Parameters

x

一个号码。

返回值

¥Return value

小于或等于 x 的最大整数。它与 -Math.ceil(-x) 的值相同。

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

描述

¥Description

因为 floor() 是 Math 的静态方法，所以你始终将其用作 Math.floor()，而不是用作你创建的 Math 对象的方法（Math 不是构造函数）。

¥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).

示例

¥Examples

使用 Math.floor()

¥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

小数调整

¥Decimal adjustment

在这个例子中，我们实现了一个名为 decimalAdjust() 的方法，它是 Math.floor()、Math.ceil() 和 Math.round() 的增强方法。虽然三个 Math 函数始终将输入调整为个位数，但 decimalAdjust 接受 exp 参数，该参数指定小数点左侧的数字应调整到的位数。例如，-1 表示小数点后保留一位数字（如 "× 10-1"）。此外，它还允许你通过 type 参数选择调整方式 - round、floor 或 ceil。

¥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.

它通过将数字乘以 10 的幂，然后将结果四舍五入到最接近的整数，然后除以 10 的幂来实现。为了更好地保持精度，它利用了 Number 的 toString() 方法，该方法以科学记数法表示大数或小数（如 6.02e23）。

¥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

规范

Specification
ECMAScript Language Specification
# sec-math.floor

¥Specifications

浏览器兼容性

BCD tables only load in the browser

¥Browser compatibility

也可以看看

¥See also