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 2015年7月.
Math.floor() 函式會回傳小於等於所給數字的最大整數。
嘗試一下
console.log(Math.floor(5.95));
// Expected output: 5
console.log(Math.floor(5.05));
// Expected output: 5
console.log(Math.floor(5));
// Expected output: 5
console.log(Math.floor(-5.05));
// Expected output: -6
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® 2026 Language Specification # sec-math.floor |
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