Math.floor()

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

Math.floor() 函式會回傳小於等於所給數字的最大整數。

嘗試一下

語法

Math.floor(x)

參數

x

數字型態。

回傳值

小於等於所給數字的最大整數。

描述

floor() 是 Math的靜態函式, 所以不需實體化Math 物件, 只要直接呼叫 Math.floor()就能使用。

(此外Math 並不是建構子).

範例

使用 Math.floor()

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

Decimal adjustment

js
// Closure
(function () {
  /**
   * Decimal adjustment of a number.
   *
   * @param {String}  type  The type of adjustment.
   * @param {Number}  value The number.
   * @param {Integer} exp   The exponent (the 10 logarithm of the adjustment base).
   * @returns {Number} The adjusted value.
   */
  function decimalAdjust(type, value, exp) {
    // If the exp is undefined or zero...
    if (typeof exp === "undefined" || +exp === 0) {
      return Math[type](value);
    }
    value = +value;
    exp = +exp;
    // If the value is not a number or the exp is not an integer...
    if (isNaN(value) || !(typeof exp === "number" && exp % 1 === 0)) {
      return NaN;
    }
    // Shift
    value = value.toString().split("e");
    value = Math[type](+(value[0] + "e" + (value[1] ? +value[1] - exp : -exp)));
    // Shift back
    value = value.toString().split("e");
    return +(value[0] + "e" + (value[1] ? +value[1] + exp : exp));
  }

  // Decimal round
  if (!Math.round10) {
    Math.round10 = function (value, exp) {
      return decimalAdjust("round", value, exp);
    };
  }
  // Decimal floor
  if (!Math.floor10) {
    Math.floor10 = function (value, exp) {
      return decimalAdjust("floor", value, exp);
    };
  }
  // Decimal ceil
  if (!Math.ceil10) {
    Math.ceil10 = function (value, exp) {
      return decimalAdjust("ceil", value, exp);
    };
  }
})();

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

規範

Specification
ECMAScript Language Specification
# sec-math.floor

瀏覽器相容性

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參見