Number.prototype.toPrecision()
Number 值的 toPrecision() 方法返回一个表示此数字的字符串，以指定有效位数表示。
¥The toPrecision() method of Number values returns a string representing this number to the specified number of significant digits.
Try it
语法
参数
返回值
¥Return value
表示给定数字的字符串，使用给定数量的有效数字。如果指数大于或等于 precision 或小于 -6，则使用科学计数法。如果省略 precision 参数，则具有与 Number.prototype.toString() 相同的行为。
¥A string representing the given number, using the given number of significant digits. Scientific notation is used if the exponent is greater than or equal to precision or less than -6. Has the same behavior as Number.prototype.toString() if the precision argument is omitted.
例外情况
示例
使用 toPrecision
¥Using toPrecision
js
// This number has exponent 0, so it will never use exponential notation
let num = 5.123456;
console.log(num.toPrecision()); // '5.123456'
console.log(num.toPrecision(5)); // '5.1235'
console.log(num.toPrecision(2)); // '5.1'
console.log(num.toPrecision(1)); // '5'
// This number has exponent -4, so it will never use exponential notation
num = 0.000123;
console.log(num.toPrecision()); // '0.000123'
console.log(num.toPrecision(5)); // '0.00012300'
console.log(num.toPrecision(2)); // '0.00012'
console.log(num.toPrecision(1)); // '0.0001'
// This number has exponent 3, so it will use exponential notation if precision is less than 4
num = 1234.5;
console.log(num.toPrecision(1)); // '1e+3'
console.log(num.toPrecision(2)); // '1.2e+3'
console.log(num.toPrecision(6)); // '1234.50'
// This number has exponent -7, so it will always use exponential notation
num = 0.00000012345;
console.log(num.toPrecision(1)); // '1e-7'
console.log(num.toPrecision(10)); // '1.234500000e-7'
规范
| Specification |
|---|
| ECMAScript Language Specification # sec-number.prototype.toprecision |
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