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true")]),s._v("\nNumber"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("isSafeInteger")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("9007199254740993")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("-")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("990")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// true")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("9007199254740993")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("-")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("990")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 返回结果 9007199254740002")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 正确答案应该是 9007199254740003")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br")])]),t("p",[s._v("上面代码中，"),t("code",[s._v("9007199254740993")]),s._v("不是一个安全整数，但是"),t("code",[s._v("Number.isSafeInteger")]),s._v("会返回结果，显示计算结果是安全的。这是因为，这个数超出了精度范围，导致在计算机内部，以"),t("code",[s._v("9007199254740992")]),s._v("的形式储存。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token number"}},[s._v("9007199254740993")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("===")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("9007199254740992")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// true")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br")])]),t("p",[s._v("所以，如果只验证运算结果是否为安全整数，很可能得到错误结果。下面的函数可以同时验证两个运算数和运算结果。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("trusty")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token 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sine）")]),s._v(" "),t("li",[t("code",[s._v("Math.acosh(x)")]),s._v(" 返回"),t("code",[s._v("x")]),s._v("的反双曲余弦（inverse hyperbolic cosine）")]),s._v(" "),t("li",[t("code",[s._v("Math.atanh(x)")]),s._v(" 返回"),t("code",[s._v("x")]),s._v("的反双曲正切（inverse hyperbolic tangent）")])]),s._v(" "),t("h2",{attrs:{id:"指数运算符"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#指数运算符"}},[s._v("#")]),s._v(" 指数运算符")]),s._v(" "),t("p",[s._v("ES2016 新增了一个指数运算符（"),t("code",[s._v("**")]),s._v("）。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("**")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 4")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("**")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 8")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br")])]),t("p",[s._v("这个运算符的一个特点是右结合，而不是常见的左结合。多个指数运算符连用时，是从最右边开始计算的。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 相当于 2 ** (3 ** 2)")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("**")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("**")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 512")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br")])]),t("p",[s._v("上面代码中，首先计算的是第二个指数运算符，而不是第一个。")]),s._v(" "),t("p",[s._v("指数运算符可以与等号结合，形成一个新的赋值运算符（"),t("code",[s._v("**=")]),s._v("）。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" a "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1.5")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\na "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("**=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 等同于 a = a * a;")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" b "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("4")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nb "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("**=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 等同于 b = b * b * b;")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br")])]),t("p",[s._v("注意，V8 引擎的指数运算符与"),t("code",[s._v("Math.pow")]),s._v("的实现不相同，对于特别大的运算结果，两者会有细微的差异。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[s._v("Math"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("pow")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("99")]),t("span",{pre:!0,attrs:{class:"token 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"),t("h2",{attrs:{id:"bigint-数据类型"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#bigint-数据类型"}},[s._v("#")]),s._v(" BigInt 数据类型")]),s._v(" "),t("h3",{attrs:{id:"简介"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#简介"}},[s._v("#")]),s._v(" 简介")]),s._v(" "),t("p",[s._v("JavaScript 所有数字都保存成 64 位浮点数，这给数值的表示带来了两大限制。一是数值的精度只能到 53 个二进制位（相当于 16 个十进制位），大于这个范围的整数，JavaScript 是无法精确表示的，这使得 JavaScript 不适合进行科学和金融方面的精确计算。二是大于或等于2的1024次方的数值，JavaScript 无法表示，会返回"),t("code",[s._v("Infinity")]),s._v("。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 超过 53 个二进制位的数值，无法保持精度")]),s._v("\nMath"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("pow")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("53")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("===")]),s._v(" Math"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("pow")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("53")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// true")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 超过 2 的 1024 次方的数值，无法表示")]),s._v("\nMath"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("pow")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1024")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Infinity")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br")])]),t("p",[t("a",{attrs:{href:"https://github.com/tc39/proposal-bigint",target:"_blank",rel:"noopener noreferrer"}},[s._v("ES2020"),t("OutboundLink")],1),s._v(" 引入了一种新的数据类型 BigInt（大整数），来解决这个问题。BigInt 只用来表示整数，没有位数的限制，任何位数的整数都可以精确表示。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" a "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2172141653n")]),t("span",{pre:!0,attrs:{class:"token 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"),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("Number")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("b"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 33334444555566670000")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br")])]),t("p",[s._v("为了与 Number 类型区别，BigInt 类型的数据必须添加后缀"),t("code",[s._v("n")]),s._v("。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1234")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 普通整数")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1234n")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// BigInt")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// BigInt 的运算")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1n")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2n")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 3n")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br")])]),t("p",[s._v("BigInt 同样可以使用各种进制表示，都要加上后缀"),t("code",[s._v("n")]),s._v("。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0b1101n")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 二进制")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0o777n")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 八进制")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0xFFn")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 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