实例方法

toExponential()

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方法返回一个以指数表示法表示该数字的字符串

function expo(x, f) {
  return Number.parseFloat(x).toExponential(f);
}

console.log(expo(123456, 2));
// Expected output: "1.23e+5"

console.log(expo('123456'));
// Expected output: "1.23456e+5"

console.log(expo('oink'));
// Expected output: "NaN"

toFixed()

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方法使用定点表示法来格式化该数值

function financial(x) {
  return Number.parseFloat(x).toFixed(2);
}

console.log(financial(123.456));
// Expected output: "123.46"

console.log(financial(0.004));
// Expected output: "0.00"

console.log(financial('1.23e+5'));
// Expected output: "123000.00"

toLocaleString()

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方法返回这个数字特定于语言环境的表示字符串。在具有 Intl.NumberFormat API 支持的实现中，此方法仅仅简单调用了 Intl.NumberFormat当格式化大量数字时，最好创建一个 Intl.NumberFormat 对象，并使用其提供的 format() 方法

function eArabic(x) {
  return x.toLocaleString('ar-EG');
}

console.log(eArabic(123456.789));
// Expected output: "١٢٣٬٤٥٦٫٧٨٩"

console.log(eArabic('123456.789'));
// Expected output: "123456.789"

console.log(eArabic(NaN));
// Expected output: "ليس رقم"

toPrecision()

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方法返回一个以指定精度表示该数字的字符串

function precise(x) {
  return x.toPrecision(4);
}

console.log(precise(123.456));
// Expected output: "123.5"

console.log(precise(0.004));
// Expected output: "0.004000"

console.log(precise(1.23e5));
// Expected output: "1.230e+5"

toString()

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方法返回表示该数字值的字符串

function hexColour(c) {
  if (c < 256) {
    return Math.abs(c).toString(16);
  }
  return 0;
}

console.log(hexColour(233));
// Expected output: "e9"

console.log(hexColour('11'));
// Expected output: "b"

valueOf()

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方法返回该数字的值

const numObj = new Number(42);
console.log(typeof numObj);
// Expected output: "object"

const num = numObj.valueOf();
console.log(num);
// Expected output: 42

console.log(typeof num);
// Expected output: "number"