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• 句法
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

toPrecision() method returns a string representing the Number object to the specified precision.

句法

numObj.toPrecision([precision])
					

参数

precision 可选

An integer specifying the number of significant digits.

返回值

A string representing a Number object in fixed-point or exponential notation rounded to precision significant digits. See the discussion of rounding in the description of the Number.prototype.toFixed() method, which also applies to toPrecision() .

若 precision argument is omitted, behaves as Number.prototype.toString() 。若 precision argument is a non-integer value, it is rounded to the nearest integer.

异常

RangeError

若 precision is not between 1 and 100 (inclusive), a RangeError is thrown. Implementations are allowed to support larger and smaller values as well. ECMA-262 only requires a precision of up to 21 significant digits.

范例

使用 toPrecision

let numObj = 5.123456
console.log(numObj.toPrecision())    // logs '5.123456'
console.log(numObj.toPrecision(5))   // logs '5.1235'
console.log(numObj.toPrecision(2))   // logs '5.1'
console.log(numObj.toPrecision(1))   // logs '5'
numObj = 0.000123
console.log(numObj.toPrecision())    // logs '0.000123'
console.log(numObj.toPrecision(5))   // logs '0.00012300'
console.log(numObj.toPrecision(2))   // logs '0.00012'
console.log(numObj.toPrecision(1))   // logs '0.0001'
// note that exponential notation might be returned in some circumstances
console.log((1234.5).toPrecision(2)) // logs '1.2e+3'
					

规范

规范
ECMAScript (ECMA-262) The definition of 'Number.prototype.toPrecision' 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
toPrecision	Chrome 1	Edge 12	Firefox 1	IE 5.5	Opera 7	Safari 2	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

• Number.prototype.toFixed()
• Number.prototype.toExponential()
• Number.prototype.toString()

元数据

• 最后修改： Jan 15, 2020

相关话题

1. 标准内置对象
2. Number
3. 特性
   1. Number.EPSILON
   2. Number.MAX_SAFE_INTEGER
   3. Number.MAX_VALUE
   4. Number.MIN_SAFE_INTEGER
   5. Number.MIN_VALUE
   6. Number.NEGATIVE_INFINITY
   7. Number.NaN
   8. Number.POSITIVE_INFINITY
4. 方法
   1. Number.isFinite()
   2. Number.isInteger()
   3. Number.isNaN()
   4. Number.isSafeInteger()
   5. Number.parseFloat()
   6. Number.parseInt()
   7. Number.prototype.toExponential()
   8. Number.prototype.toFixed()
   9. Number.prototype.toLocaleString()
   10. Number.prototype.toPrecision()
   11. Number.prototype.toSource()
   12. Number.prototype.toString()
   13. Number.prototype.valueOf()
5. 继承：
6. Function
7. 特性
   1. Function.arguments
   2. Function.caller
   3. Function.displayName
   4. Function.length
   5. Function.name
8. 方法
   1. Function.prototype.apply()
   2. Function.prototype.bind()
   3. Function.prototype.call()
   4. Function.prototype.toSource()
   5. Function.prototype.toString()
9. Object
10. 特性
    1. Object.prototype.__proto__
    2. Object.prototype.constructor
11. 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()