(window.webpackJsonp=window.webpackJsonp||[]).push([[1713],{2121:function(t,s,a){"use strict";a.r(s);var n=a(31),e=Object(n.a)({},(function(){var t=this,s=t.$createElement,a=t._self._c||s;return a("ContentSlotsDistributor",{attrs:{"slot-key":t.$parent.slotKey}},[a("h1",{attrs:{id:"built-in-constants"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#built-in-constants"}},[t._v("#")]),t._v(" Built-in Constants")]),t._v(" "),a("h2",{attrs:{id:"null"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#null"}},[t._v("#")]),t._v(" null")]),t._v(" "),a("p",[a("code",[t._v("null")]),t._v(" is used for representing the intentional absence of an object value and is a primitive value. Unlike "),a("code",[t._v("undefined")]),t._v(", it is not a property of the global object.")]),t._v(" "),a("p",[t._v("It is equal to "),a("code",[t._v("undefined")]),t._v(" but not identical to it.")]),t._v(" "),a("div",{staticClass:"language-js extra-class"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("null")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("==")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("undefined")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// true")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("null")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("===")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("undefined")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// false")]),t._v("\n\n")])])]),a("p",[a("strong",[t._v("CAREFUL")]),t._v(": The "),a("code",[t._v("typeof")]),t._v(" "),a("code",[t._v("null")]),t._v(" is "),a("code",[t._v("'object'")]),t._v(".")]),t._v(" "),a("div",{staticClass:"language-js extra-class"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typeof")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("null")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 'object';")]),t._v("\n\n")])])]),a("p",[t._v("To properly check if a value is "),a("code",[t._v("null")]),t._v(", compare it with the "),a("a",{attrs:{href:"http://stackoverflow.com/documentation/javascript/208/boolean-logic/798/strictly-equal#t=201606190429161299094",target:"_blank",rel:"noopener noreferrer"}},[t._v("strict equality operator"),a("OutboundLink")],1)]),t._v(" "),a("div",{staticClass:"language-js extra-class"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" a "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("null")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\na "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("===")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("null")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// true")]),t._v("\n\n")])])]),a("h2",{attrs:{id:"testing-for-nan-using-isnan"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#testing-for-nan-using-isnan"}},[t._v("#")]),t._v(" Testing for NaN using isNaN()")]),t._v(" "),a("h3",{attrs:{id:"window-isnan"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#window-isnan"}},[t._v("#")]),t._v(" "),a("code",[t._v("window.isNaN()")])]),t._v(" "),a("p",[t._v("The global function "),a("code",[t._v("isNaN()")]),t._v(" can be used to check if a certain value or expression evaluates to "),a("code",[t._v("NaN")]),t._v(". 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