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• 句法
• 描述
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

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

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

句法

Math.floor(x)
					

参数

x

A number.

返回值

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

描述

因为 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).

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

范例

使用 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
					

Decimal adjustment

/**
 * 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
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

规范
ECMAScript (ECMA-262) The definition of 'Math.floor' in that specification.

浏览器兼容性

The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
floor	Chrome 1	Edge 12	Firefox 1	IE 3	Opera 3	Safari 1	WebView Android 1	Chrome Android 18	Firefox Android 4	Opera Android 10.1	Safari iOS 1	Samsung Internet Android 1.0	nodejs 0.1.100

图例

完整支持

完整支持

另请参阅

• Math.abs()
• Math.ceil()
• Math.round()
• Math.sign()
• Math.trunc()

元数据

• 最后修改： Jan 15, 2020

相关话题

1. 标准内置对象
2. Math
3. 特性
   1. Math.E
   2. Math.LN10
   3. Math.LN2
   4. Math.LOG10E
   5. Math.LOG2E
   6. Math.PI
   7. Math.SQRT1_2
   8. Math.SQRT2
4. 方法
   1. Math.abs()
   2. Math.acos()
   3. Math.acosh()
   4. Math.asin()
   5. Math.asinh()
   6. Math.atan()
   7. Math.atan2()
   8. Math.atanh()
   9. Math.cbrt()
   10. Math.ceil()
   11. Math.clz32()
   12. Math.cos()
   13. Math.cosh()
   14. Math.exp()
   15. Math.expm1()
   16. Math.floor()
   17. Math.fround()
   18. Math.hypot()
   19. Math.imul()
   20. Math.log()
   21. Math.log10()
   22. Math.log1p()
   23. Math.log2()
   24. Math.max()
   25. Math.min()
   26. Math.pow()
   27. Math.random()
   28. Math.round()
   29. Math.sign()
   30. Math.sin()
   31. Math.sinh()
   32. Math.sqrt()
   33. Math.tan()
   34. Math.tanh()
   35. Math.trunc()
5. 继承：
6. Object
7. 特性
   1. Object.prototype.__proto__
   2. Object.prototype.constructor
8. 方法
   1. Object.prototype.__defineGetter__()
   2. Object.prototype.__defineSetter__()
   3. Object.prototype.__lookupGetter__()
   4. Object.prototype.__lookupSetter__()
   5. Object.prototype.hasOwnProperty()
   6. Object.prototype.isPrototypeOf()
   7. Object.prototype.propertyIsEnumerable()
   8. Object.prototype.toLocaleString()
   9. Object.prototype.toSource()
   10. Object.prototype.toString()
   11. Object.prototype.valueOf()
   12. Object.setPrototypeOf()